According to the blog below, Vista is doing well in the consumer market. There has been significant resistance, however, on the part of small businesses.
http://blogs.zdnet.com/Bott/?p=349&tag=nl.e590
As noted by Barbara, hardware requirements are rather steep compared to XP. And I question the decision to release it in so many flavors. Install discs, as opposed to OEM licenses, are pricey as well. [shrugs]
One should keep in mind that the vast majority of computer buyers don't care much, they just want their computer to work and perform their accustomed tasks. Most buy a new computer without thought as to which OS is on it, so long as it's the familiar Windows. And no OEM has gone out of their way to make plain to them they can still choose XP, even Dell.
I don't hate Vista, but I'll give it a pass. If you ask yourself what an OS is for, the answer is to run the programs you need, it's not an end in itself. XP is perfectly adequate for now. If all my video editing/encoding programs worked well enough on Ubuntu, I'd ditch Windows entirely.
Learning how to use Linux equivalents is time consuming, and I confess I haven't made much progress there.
The first service pack for Vista should fix most of the problems it's had.