I have been using Vista for the past 6 months on 2.0GHz, 4 GB RAM laptop. I have to say even with this configuration it is as slow as snail. Feature wise it takes the points but for its speed I hate using it. I use XP in my office with not even half the configuration and it runs like a hare. Microsoft has to do something to get it running faster.
It has got some interesting useful features. The quick search option. It gets you the files you are looking for in a flash. But the say we can accomplish by installing google desktop. The Aero feature - probably this is the culprit for using so much memory and CPU. Though it looks good believe in the past 6 months I havnt used it even 10 times. Its just a useless feature we can live without.
I still havnt found any useful feature that vista has and XP doesnt. My laptop came preloaded with Vista otherwise I would have gone for XP for sure.