Eclipse quit unexpectedly (Mac OS X 10.7.4 and Eclipse 3.8)
This is probably because eclipse shutdown abnormally.
Open the Terminal and go to the location where eclipse is installed.
Then run eclipse from the terminal like...
$./eclipse -clean

It should start, once it does go to the Eclipse menu and Quit eclipse.
If you have any shortcuts on the desktop you'll have to remove them and make new shortcuts with the executable.