An application doesn't run anymore...

If an application doesn't run anymore or seems blocked on a message displaying "Caching Fonts", you have probably removed the Fonts Cache.

In this case, don't force the application (or X11) to quit, please wait...

Indeed, the rebuilding of Fonts Cache in some Open Source applications (Gimp, MPlayer OSX Extended...) is particularly long.
Once the Cache rebuilt, the application will launch again normally.