Microsoft could be losing billions of dollars in terms of lost earnings because Vista is not backwards compatible with Windows XP. As a result, businesses are not risking upgrading from Windows XP. Mainstream support for XP ends on April 14, yet most businesses are likely to carry on using it because they cannot be certain mission applications will run in the more secure Vista environment.
Last April when Allan Krans, an analyst at Technology Business Research, looked at the Q4 2007 revenues in the Microsoft client division, he noted that it fell 24%. This compares to 2002, when XP was shipping where the fall for the same period was only 1%.
Microsoft may well have shipped many copies of Vista, but I think few corporates are buying it, and fewer believe it will run their enterprise apps. This is the true cost of its trustworthy computing initiative, to develop secure software.