#1 reason I'm still with SL.
Expose + Spaces. Mission Control sucks.
I have only started using multiple desktops in Lion. Spaces somehow never clicked with me. I did really enjoy Exposé though, but one of the things I liked most about it was the fact that its original version from the Panther and Tiger days kept relative window sizes intact, and generally used the screen space more efficiently than Exposé from Leopard on. I feel like Mission Control, considering the Spaces integration, is overall an improvement over the Leopard/SL version of Exposé, since relative window sizes have returned, picking out windows belonging to applications with 1-3 windows open among applications with huge amounts of windows has become much easier, and windows are possibly easier to identify by being able to see the associated app icon. My usage has shifted so that I now use App Exposé much more often for apps with lots of windows open. Mission Control stops making sense in that case unless the app's window you're looking for is one of the most recently used ones.
If only Mission Control actually spread out the Windows instead of moving them 25 px.
Yeah, I'm still kind of baffled by their decision to implement it like that, since the solution scales so badly with the number of windows not quite sure what they were going for there
EDIT: I just realized that you probably weren't talking about the view you get when you perform the scrolling gesture over a window group that's what I was thinking of. If they changed that to an App Exposé style view, that would be an improvement in my book.
EDIT2: Or, you know, just give us an option to decide for ourselves whether we want to see our windows grouped by application or not. But I guess that's not how Apple rolls...
I agree that the grid set up of 10.6 was a big step backwards and preferred the 10.5 proportional layout. Luckily there was a really simple hack to bring back a 10.5 style Expose in 10.6. If only Mission Control actually spread out the Windows instead of moving them 25 px.