If you want to see what I consider a pretty cool use of swapping targets from a devicemapper device while it is mounted, check out the ZyX Rebootless LiveOS Installer, now available in the fedora-11 updates repository (zyx-liveinstaller).
Short story, its like the normal Fedora LiveCD/USB installer, except you don't need to reboot after installation completes to start/continue using your now installed/non-live system.