There's an update for livecd-tools in f15-updates-testing that is needed in order to create F17 usb installers.
https://admin.fedoraproject.org/updates/FEDORA-2012-3090/livecd-tools-15.12-...
If anyone has an F15 box around and can test, it would be great to get that pushed to stable soon so that F15 users can create bootable USB sticks for F17 more easily.
Tim