There was an interesting article that talked about an 'experiment' that Microsoft did. They took 120 people who previously said "I don't like Vista". They put them in a room and had them try out a brand new operating system called "Mojave". Afterwards, they revealed to them that they were actually using Vista (minus any identifying logos). Those peoples average rating of Vista went from 4.4 (unfavorable) to 8.5 (out of 10).
Most were XP users. About 22% were Mac users (insert devious giggle here).
I've been using Vista for quite a while with very few problems (especially post-SP1), and I prefer it over XP. Perhaps more people should actually TRY it before they dismiss it. :)
Update 8/17/08 - found Microsoft's website for the Mojave experiment.