I've had two sets of related experiences:

- Facebook icon was missing and wouldn't appear even after theme changes, uninstall and reinstalls, and a full wipe. It appeared in App World > My World, but still wouldn't run. I upgraded to 4.5 and it worked.

- Now in 4.5, I misplaced the Google App while trying to move it out of the Apps folder. Changing themes made it accessible, but then changing back to the original theme made it disappear again. Sigh. So I'm staying with the new theme for now.