This happens whenever I switch back from Target Display Mode. For every application open.
Or try connecting to a Lion share from a windows computer.
They may be two small issues to most, but they are huge issues to me. Everytime I want to switch over to my PC I have to make sure I close every single application so that it doesn't resize the eff out of them. Want to connected to my shared folders on my iMac from my gaming machine, nope.
Spaces I don't mind. It is pretty much the same as before just visually different.
I like Mail. I really like the improved Mac-to-Windows SMB file sharing.
Otherwise I find it pretty much exactly the same.