I am a big fan of Win7, if I hadn't switched to a Mac 4 years ago, I would have been totally happy with it. But I feel like I can do more things on my Mac, layering windows and getting at them more easily through a combination of Spaces and Expose (and the stuff that is coming in 10.7).
Really love AeroPeek, and if the AeroSnap worked better I would love it too (aerosnapped windows do not remember their settings after they are closed or you reboot, and you can only do half the screen when you drag to the side). The new taskbar is great, and the rest of the OS is pretty snappy.
Also, Magic Trackpad is pure gold. Seriously, it is wicked. A little weird using a trackpad on a desktop, but it is pretty awesome.