Mission Control is apparently still tied to the Dock process. So to restart it go to Terminal and type:
killall Dock
As with previous OS X version, this will restart the Dock and Expose/Mission Control. This isn't really a new hint. More of a confirmation that this technique still works in Lion.
[crarko adds: No, not new or earthshaking. But sometimes it's comforting to know that old techniques are still applicable to new features.]

