odd, has happened twice. here's what happens:

I type in a link which takes years to come up. Bored, I navigate my
bookmarks for something else. If, while navigating, the request times out
and the little "request timed out" box pops up, X is dead to the world. I
can move the mouse and see it move, but cannot click on anything, switch to
another viewport, or switch to another program. No menus, no nothing. I can
switch to a text console, but when I come back to X its still dead.

Only solution is to kill the x server and login again.

I've had this twice now ... the first time it seemed so unbelievably
bizarre i didn't dare post it.