Mac OS X Lion GET!
First impressions: Awesome (is my fanboy showing?)
First thing I did was to reverse the mouse scrolling direction. It is fine on the touchpad (or a touchscreen device), but not with my Logitech mouse. (uh oh, I don't have Magic Mouse)
Launchpad definitely cleans up the mess and makes things all tidy. You can organize things in folders just like on iOS. But there's no shortcut to bring up Launchpad by default. You can set up a Hot Corner instead: System Preferences > Mission Control > Hot Corners (button at the bottom).
Mission Control is Exposé + Spaces combined, and seems to be a lot nicer and more functional. You can also switch between spaces using three finger horizontal swipe. It is very smooth and makes spaces a lot more accessible.
Each fullscreen app goes to its own "space", so to speak, which makes it possible to switch between them using the same horizontal swipe. It is a very cool idea, and I remember seeing it in a video a few years back as a prototype OS UI design - which I cannot seem to find at this moment. Gotta hunt it down and bring it back from the depths of the internet.
There are many more features and numerous enhancements. One of them is the Resume feature. Ability to hibernate and resume applications in an isolated manner sounds awesome.
That's it for a quick review! Hope to post more updates, especially after Xcode 4.1 installs!