Hm, I've just played with a copy of Win 7 on a friends Macbook Pro (in VMWare). As the VMWare drivers aren't tuned, Aero was not working. My friend said he thought Win 7 was faster than Vista, though it is well known that Vista hates virtualisation.
Dropping memory down to 512MB, Win 7 is still nicely responsive. That is not the case doing the same with a Vista VM.
I do much prefer the taskbar to XP and Vista, having launch and task management unified is much more intuitive to me. As we had no aero, all the sexy features were not available (which cripples the task bar substantially IMO), and to be honest the overall experience was underwhelming, it really feels like Vista SP3 UI wise. Moving windows to the edge to resize them is nice. Though some have commented that the beta is stable, we constantly froze it using Java 6, and windows experience index would always fail to complete.
One thing I loved compared to Vista - I always put my utilities like process explorer in a directory "Accessories" in "Program Files". Vista made this amazingly irritating with UAC enabled. Win 7 handled it fine, bravo!
I'm sure I'm missing some of the smaller tweaks here and there (I think there are many of the poor UI design bits fixed), Win 7 was nice, but underwhelming. I think it *is* clearly better than Vista resource wise (which is not saying much IMHO).