After installing F15 Alpha RC2 into a virt-manager VM and booting the installed system and logging in (resulting in the fallback desktop), there's a broken quicklaunch to the left of the (working) Evolution quicklaunch in the top panel. It displays the 'platform on a spring' icon that I believe represents quicklaunchers in general, left-clicking it gives a 'Could not launch appplication' error, and right-click / Properties shows no Name, Command or Comment.
This I propose blocks Beta: "No part of the default desktop's panel (or equivalent) configuration should crash on boot of the installed system using default installation choices" - that criterion is a little too tightly worded, it should also cover default panel configuration items being obviously non-functional.
I noticed after updating the test system to post-Alpha stuff (big changes to gnome-panel etc), the broken launcher went away. I'll test with the GNOME Test Day image to be sure it's gone on a fresh install of later packages too, but I think this is fixed. Setting MODIFIED.
Discussed at 2011-03-11 blocker review meeting, accepted as a blocker as per above criterion.
confirmed fixed in current nightly.