I tried to format the USB flash disk as FAT filesystem using palimpsest (that belongs to gnome-disk-utility package), but it only gave me unhelpful error saying that it was unable to execute mkfs.vfat process. After installing sys-fs/dosfstools everything went a bit smoother ;)
I would handle this with an use flag. Not everybody want's to have dosfstools installed. Is there a meaningful use-flag you would suggest?
+*gnome-disk-utility-2.30.1 (13 Jun 2010) + + 13 Jun 2010; Pacho Ramos <pacho@gentoo.org> + +gnome-disk-utility-2.30.1.ebuild, metadata.xml: + Add new version for Gnome 2.30. Also fix bug #300620 (thanks to Priit Laes + for reporting) adding a 'fat' USE flag like sys-block/gparted.