Alt-F2 brings up the command run dialog.
In the past it would auto-complete the command you are typing based upon stuff in $PATH. A few days ago it seemed to have stopped doing auto-complete.
Still works fine here.
If I completely disable ibus, this problem goes away. This seems to be a mild form of problem similar to Bug #492956, which started with the attempt to fix Bug #491999.
Fixed in ibus-1_1_0_20090407-1_fc11. Please test it.