To be fair, I haven't installed the retail version of Vista on this pc. I've only installed the last beta version of Vista Ultimate and XP Home. My impression of Windows 7 is that the desktop is very responsive. It easily matched XP Home and that's having Aero features fully enabled. The Vista beta I tried before needed some compromises.
It's speedy alright. I do have some gripes. Personally, I think MS should've kept the classic Start Menu as an option. Win7's Taskbar and Start Menu seems much less functional than in previous versions of Windows. The Start Menu doesn't expand much anymore. I now have to scroll around which I dislike.
Overall, I like the responsiveness. Although I wish MS kept most of Vista's features, I'd still buy Win7 when it's released.