Filesystems with Transactions?

Bryan Andersen asks: "I'm looking for a filesystem that I can rollback all the changes made by a user to a given date/time. Are there any for Linux or *BSD, or is my only option to go to one of the NAS vendors? I want this so I can more easily cleanup after users trash all the files they can access. Yes I know this would mean I'd have to have much larger partition sizes, but I feel with disk prices the way they are I can't go wrong doing this." I'm not aware of any filesystems that can specifically do this, and I'm not quite up on my JFS knowledge to know if any of those can be adapted to this task without code changes. It would seem like the easiest way to do this would be to mirror the drives at set times (your "commit") and then a "rollback" would be a simple matter of restoring from those images. Of course, there may be just such a file system in the works that I simply haven't heard about yet. Have you?