After being asked by a user in #ubuntu-no on Freenode IRC if there was a method of restoring his system, I researched if the underlying things needed to implement this was present (always curious...). While LVM has had snapshots for a long time, being able to merge a snapshot back into its origin has been missing. Some 15 minutes of googling showed that initial work on this was done in August 2008, so strange if it hasn't been completed yet? Turns out it has, so the strange part is that none of the Linux news sites have written about it (that I've seen).
The required kernel bit, a "merge target" in the DM layer, was merged in the just released linux 2.6.33 and the lvm parts are there from 2.02.58. LVM can now do snapshot merging with lvconvert --merge! I'm assuming here that the device-mapper code thats in between those two components has also been finished and released, which ought to be a safe assumption.
This makes me wonder why Fedora has chosen to base their System Rollback feature for Fedora 13 on btrfs instead of LVM, which would work on any file-system. There are probably good reasons.