Writing this on a pc running Vista RC1, and there are some things which have improved greatly since XP, and others which have become worse. Some of the "new" *cough*Tiger*cough* features are nowhere near as good as the OS X equivalent. Vista's search is a joke compared to Spotlight, and there is a bad attempt to do something a bit like Exposé, but it's not really useful.
That being said Vista was able to find all the necessary drivers for my PC, very impressive considering the time it takes me to install all my drivers after reinstalling XP. There is also a nice feature that shows a small window with the program when you mouse-over in the task bar. It looks better than XP, but it's still "too much" somehow.
It's less intuitive, and to be honest it does not seem as if it's been built from the ground up. For instance the "Install new font"-feature still looks exactly like it did in win 95 (almost 3.11) - that thing hasn't changed in any version of Windows!
Of course the gamers will like DirectX 10...
I wont start comparing Vista to Leopard, as it doesn't even hold up to Tiger the way I see it.
I for one am looking forward to getting my Macbook Pro, so that I can get back on OS X.