Windows 7 is pretty good. Not perfect, but good. And definetly better than WinVista.
And nowadays there is not much to say against Vista. Its big problems are fixed (finally...), no more perfomance problems, no more giant security holes. Actually, it offers better security (especially for non-power users).
I personally never liked Vista. Since the day it was announced with that weird glossy transparency style to the day I finally got it preinstalled on the notebook I bought. Couldn't bear with it longer than a week (I really tried to give it a chance!). Constantly being asked "are you sure you wanna open that file", "are you REALLY sure you wanna open the file?" annoys as hell (first thing I had to turn off, but apparently together with all the other security goodies of Vista...). Horrible usability due to the transparency style which still used a lot of space on screen being quite "blocky"...
The horror...
Win7 is a good alternative, its recent betas are incredibly stable compared to the first WinXP and Vista versions. I'm just waiting for more official Win7 drivers and software to be released. Until that, Win7 remains my second boot partition
. though it has good backwards compatibility, you can use most WinXP/Vista drivers on Win7 if nothing else is avaible, and most programs run in compatibility mode. Better than in Vista, that is 
.