Two things I'm missing:
* a quick way to summon the activities tab for a search (which is how I start most apps)
* Ubuntu's special applets, what are they called, the indicator and the me menu?
I really do miss the "Me Menu" though. Here's hoping Lucid can integrate it with Gnome Shell somehow.
Other than that, it's a blast. I've really taken to snapping the mouse to the upper left to get that Expose-like windows discovery, and its pretty much replaced ALT-TAB and minimizing windows for me. The transition is fast and smooth; ALT-TAB feels especially clumsy after discovering windows this way.
I'm not too sold on the "sidebar" though (click your name, then click 'sidebar' to see it). Doesn't seem to do anything more than moving to the activities tab, and given how fast "Activities" responds to a quick mouse flick I'm not sure I'd even use the sidebar. I haven't been, so far.
Could definitely do with a smaller "recent items" and a bigger "applications" / favorite space, too.
Anyway, enough rambling. I have to go fix this "mysteriously broken" Vista laptop. You like that, yeah? "Mysteriously broken?" 'Cuz I sure as hell don't.