Founded in December 2002 and launched in May 2003 it is one of the oldest professional networking sites, and its core service has remained free of charge. As of January 2008, it had more than 18 million registered users across the spectrum of industries, with five million of them being in Europe.
It competes with Ryze, XING, Plaxo, Yahoo! Kickstart and, the social networking site Facebook, among others. However, LinkedIn is centred on helping its users to capitalise on their business contacts, and features searching capabilities that allow users to find jobs, contacts and answers to business queries.
Kevin Eyres, LinkedIn managing director for Europe, says that LinkedIn aims to make its time-poor users more productive by giving them the means to make the best use of their business connections.
The website originated in Silicon Valley, and reached a million users relatively quickly because of its roots in hi-tech, new media and venture capitalist communities, says Eyres.
Although many of today's users are in IT and new media, it is seeing rapid growth in sectors including education and management, research, hospital and healthcare, construction, retail, financial services, law, insurance and oil, he says.
From a technology standpoint, LinkedIn provides a framework and structure for its users to create and display content, and this is the essence of Web 2.0, says Eyres. Beyond that, it is down to the user to build his or her network, and capitalise on it, he says.
Mike Reid, UK managing director of global services firm Sapient, says, "Part of LinkedIn's success lies in its easy-to-use design, offering a useful means of extending business relationships."
Reid adds, "LinkedIn's fundamental value is in the quality of contacts that it offers. However this integrity is dependent upon the way that it is used. Simply adding as many contacts as possible will only leave you with an expansive contact database that in real terms is of little use."
Reid believes that LinkedIn has become the main means of keeping in touch with business contacts in the UK and worldwide, but says that for more interactive communications, he recommends social networks such as Twitter.
Another user, Andrew Fawcett-Wolf, managing director of Thrive Digital, says he has been a big fan of the site from the beginning, when he was contacted by a company that wanted to use his firm's services. Since then, he has gathered innumerable contacts through LinkedIn.
"The primary reason I use it is because it has generated pre-qualified business leads for my business - that is companies that need my company's products and services that have reached out to ask me for help. Having realised this, I have continued to make a concerted effort to maintain and raise my profile on the site."
"The second reason is when I want to reach out to a prospect or potential partner/supplier - it is a great way of contacting the right person or group without going through the generic 'contact us' methods."
Commenting on the technology behind LinkedIn, Satnam Brar, managing director of specialist ERP recruiter Maximus IT, says, "The Web 2.0 technology has revolutionised the way we communicate and has made it easier than ever before to keep in touch and share information with a wide range of people. I am a LinkedIn user and think that sites like this benefit all.
"How would you ever have such easy access to this large number of professionals without tools like these online networks? You never know when tapping into your extended network can prove to be a real helping hand in your career, your business or any other aspect of your life."
However, one slightly more sceptical user, Chris Gledhill, managing director of enterprise software company PDMS, says, "Personally I think the technology is pretty impressive but I am not sure how much value it creates in practice.
"The real challenge for something like LinkedIn is volume: achieving a critical mass. That means [creating a situation where] it's odd if you are not a member, versus the natural scepticism of busy people who may view it as a spammer's charter. For what it's worth, I am a member but I don't use it unless it is to respond to an invitation to join someone else's network which I tend do out of politeness."
"One of the biggest problems with social networking is deciding where the boundaries lie between people's personal and work lives," says Philip Szomszor, tech blogger and head of client services at public relations agency Berkeley PR.
"For example, do you want your boss or client as your 'friend' on Facebook? Is Facebook or LinkedIn a work or social tool? One business associate I knew created a Facebook group to use as a project management/discussion tool, but was surprised that people were resistant to join. Unfortunately social networking websites aren't yet sophisticated enough to understand context, but this will arrive in time."
He adds that in terms of the recent Web 2.0 technology additions to LinkedIn, the firm "seems to be clutching at straws".
"LinkedIn seems to have realised that the site had become a bit of a Panini sticker album, where members collected contacts without there being an end goal or benefit in sight. So, the danger is that it becomes bloated with extra functionality without delivering value for the time people invest in it."
But Szomszor says, "Despite the potential sticker album nature of collecting contacts, LinkedIn does work nicely as a simple online address book and CV/profile tool. I've not met anyone that's won business from it, but I've managed to stay in touch with people that have moved around jobs. What I like about LinkedIn is that it's 'work' focused, leaving the likes of Facebook, MySpace and so on for the stuff that you do in your spare time."
Will McInnes is a LinkedIn user and managing director of social media agency Nixon McInnes, which works with brands such as BMW, O2 and Fat Face. He says, "The technology is growing in utility from relatively basic to potentially more interesting.
"The only real 'Web 2.0' innovation on LinkedIn to date has been 'Recommendations' which is good 'ratings & reviews'-type functionality that aims to provide more context and trust than a traditional CV."
David Lavenda, vice-president of marketing and product strategy of WorkLight, a provider of secure Web 2.0 systems, says that LinkedIn's Web 2.0 technology would be even more useful if the firm opened up the platform to third-party developers.
"Web 2.0 implies user-defined content, a high degree of personalisation, an interactive experience, and so on. Allowing third parties to leverage the LinkedIn social graph would make it much more valuable."
"For example, opening up the APIs has propelled Facebook to a position of prominence in the social networking world. Web 2.0 tools can be used securely in the enterprise, if the proper infrastructure is in place," he says.
Example of a real LinkedIn business network
LinkedIn member: Six years.
Uses LinkedIn for: Keeping in touch with ex-colleagues, particularly abroad. Also useful for looking for jobs and project collaborators.
Comment: "The new picture option has been a shocker in some ways: there are lots of contacts I haven't met face to face, and it's quite novel to put a face to a name, but suddenly it made it feel like Facebook!"
LinkedIn member: Three years.
Uses LinkedIn for: Keeping in touch with the network HR purposes approaches from candidates, clients, prospects and even headhunters/recruiters.
Comment: "We needed to wait to find the best business network as there was the apparition of quite a few in recent times. Eg. openBC and Xing."
LinkedIn member: Two and a half years.
Uses LinkedIn for: Very little.
Comment: "I haven't seen a professional approach on LinkedIn yet, compared to Xing, where I have more professional contacts. At present, LinkedIn would get an "annoying"-grade from me, not as high as Facebook, but it's heading that way.
LinkedIn Name: Joshua.
LinkedIn member: Two years.
Uses LinkedIn for: Finding the right people and resources for various projects involving online marketing, publishing, learning and management consulting. Found LinkedIn an ideal channel for word-of-mouth marketing.
Comment: "LinkedIn, unlike MySpace or Facebook, has set a professional (as opposed to personal/entertainment) stage for dialogue and thought leadership. I appreciate the opportunity to collaborate."
LinkedIn Name: Dave.
LinkedIn member: One and a half years.
Uses LinkedIn for: A networking platform to find people and connect with them.
Comment: "It is useful but I do not use it proactively. I prefer Xing which is a German networking platform."
LinkedIn Name: Liam
LinkedIn member: One year.
Uses LinkedIn for: Communicating and collaborating with people around the world, and for the questions and answers tool.
Comment: "I have tried a quite a few alternatives like Xing, ecademy and others but I much prefer LinkedIn. For me, LinkedIn is the real extension of the theory that world is flat. I have helped people in the US and Canada by introducing my contacts who are in the US and Canada!"
LinkedIn Name: Zeljko
LinkedIn member: Two years.
Uses LinkedIn for: Keeping in touch with the network and keeping on top of changes in roles and positions at partner and client companies.
Comment: "I've certainly had a number of head hunter, job offer and collaboration contacts. LinkedIn definitely sets a professional tone. It encourages professional behaviour, whereas some other networking tools lend themselves to more social nonsense use, and abuse."
LinkedIn Name: Thomas
LinkedIn member: One year
Uses LinkedIn for: Building a contact network, and keeping in touch with business contacts.
Comment: "It has helped me to reconnect on the new business front. To be honest, I haven't used all of LinkedIn's services, so I'm not using it to its full potential."
LinkedIn Name: Eileen
LinkedIn member: A year.
Uses LinkedIn for: Finding other professionals to network and share knowledge with. Also to reconnect with former colleagues, friends and business partners.
Comment: "LinkedIn offers a professional face to the social craze, it is a basic and simple business networking site. There are some with more functionality, such as Viadeo, so I use both."