Seems to me that every new OS release brings cries of “but we love the old stuff!”. This article from Computerworld puts some numbers on that. It’s a good read..

http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=324685

The other issue that we have with each OS is that we use all the capabilities of existing machines (and then some). I remember the outcry with the release of Windows 95 when we recommended 8mb of memory and a clock speed of 20mhz. It didn't take long for that to be a minimum spec machine.

Having said that, it seems that our customers are saying that maybe we turned the dial a step too far for both the device compatibility bar and hardware utilisation. The hardware compatibility requirements seem to have been (mostly) solved (though I could see why it's still pretty hard to convince the manufacturer of a $70 printer to spend a lot of money updating drivers for no extra revenue). And apparently Windows 7 is aiming at getting some performance gains (see http://www.infoworld.com/article/08/08/28/Performance_improvement_integral_to_Windows_7_IE8_1.html). And yes, it is amazing how much processor and memory Outlook uses. 

From the anecdotal evidence, it seems to be: if your PC (with at least 2GB of memory!) and attached devices are certified for Vista, then you'd be one of those many people who love Vista. But if you've never used Vista and don't like change, then it'll take a few more years for you to move. Same as it ever was.