All auto mounted fat devices are now mounted without setting the relevant user. The effect is that files are owned by root and the current user cannot write to the device. IOW, the auto mount feature is close to useless. :(
Is this more fallout from the gnome-mount bustage ? Do you have gconf keys below /system/storage/default_options/vfat ? If not, can you try to uninstall and reinstall gnome-mount ?
Ah, I talked to Pierre yesterday on #hal @ Freenode; reinstalling gnome-mount made it work. And he said I could close this bug. Soo...