Menu bar frozen / stuck in one app

I just wrote a reply to exactly the same issue in Snow Leopard:

http://discussions.apple.com/thread/3016997

Since for me the problem first appeared after installing Lion, I feel i have to start a new thread here.

It is definetely not related to any special piece of (third party) software, since it can happen in any application.

The windows of all other applications are still usable, but appear inactive (grey controls).

So it appears as if the UI of the frontmost app is frozen (usually it does not have any visible windows).

The workaround I also described in the SnoLeo thread:

Closing the lid of the MacBook Pro (late 2008) once for a few seconds gets You out of this state. I guess the same thing could be achieved by putting your machine to sleep in any other possible way, but I haven't tried that yet.

Of course I had tried all the usual stuff like repairing the disk and fixing permissions several times before to no avail.