Somewhere post-F10, metacity lost the ability to update icons on already created (mapped?) windows. It keeps the icon it had initially forever. This is noticable in applications that set their icon after being mapped as well as those that change depending on what they're doing. A good test is to start ooffice and create a new document. The taskbar will reflect the new document type icon, but metacity will show the old generic OOo icon.
I should mention that a debug dump from metacity shows that it is getting the notifications that _NET_WM_ICON has changed, it just doesn't do anything about it.
Ping! This should probably be fixed before F11.
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle. Changing version to '11'. More information and reason for this action is here: http://fedoraproject.org/wiki/BugZappers/HouseKeeping
In F12, it works for fine for me with OpenOffice as described and also with previews in the GIMP. I think it might have been the upstream bug https://bugzilla.gnome.org/show_bug.cgi?id=572573.