Apple sold more than 300,000 iPads on the day of its launch in the US, and new owners downloaded more than three applications and "almost a book" within hours of acquiring it.
But TechCrunch blogger Michael Arrington reported users were frustrated by poor or non-existent Wi-Fi access where other Apple Wi-Fi devices worked. There were no reports of problems with the iPad's 3G mobile telephony access.
Apple has not yet commented on the problem, but analysts say poor Wi-Fi access could be a sales killer.
According to reports, there are more than 3,000 iPad apps available at the App Store, but only 20% are free.
iPads should be available in the UK later this month.
Meanwhile, Apple has invited journalists to a preview later this week of its new iPhone operating system. It is expected to allow third-party applications to run in background mode. If true, it would make iPhones and iPads more useful, allowing it to run more than one application at a time.