During the first year its available, Windows Vista is expected to be sold 90 million times:
To put that number into perspective, Microsoft shipped about 67 million copies of Windows XP, in the year after the software's launch on October 25, 2001. If Microsoft can achieve IDC estimates, the company would see a 34% gain over first-year XP shipments. That number, of course, also is due to an increased number of potential customers worldwide. Ovum analyst David Mitchell recently said that he would expect a similar percentage of XP users to transition to Vista as 2000/Me users to XP five years ago. According to Mitchell about 12-14% of PC users migrated within one year and he expects about 15% of today's PC users to switch to Vista in the same time frame.