In current Rawhide (Shell 3.1.3), the alt-f2 run dialog is broken: anything you enter comes up as "command not found". (Also, I was just testing to see what would happen if I specified an explicit path, and that's fun: I entered '/usr/bin/gnome-terminal' , and it got stuck with the 'Please enter a command:' dialog displayed and the rest of the interface part-greyed-out...)
Reported at https://bugzilla.gnome.org/show_bug.cgi?id=656054 Confirmed with version 3.1.3 and 3.1.4 on Ubuntu development & Fedora 16.
This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle. Changing version to '19'. (As we did not run this process for some time, it could affect also pre-Fedora 19 development cycle bugs. We are very sorry. It will help us with cleanup during Fedora 19 End Of Life. Thank you.) More information and reason for this action is here: https://fedoraproject.org/wiki/BugZappers/HouseKeeping/Fedora19
Closing this one, as the alt+f2 run dialog works correctly in current versions of Fedora.