Daniel Phillips, the guy behind Zumastor and ddsnap, csnap, RamBack and many other brilliant developments is doing it again: yesterday he announced the tux3 versioned filesystem (as opposed to ddsnap, which was a software layer on top of any other filesystem) which uses versioned pointers instead of copy on write.
He has also written a preliminary comparison with the HAMMER filesystem by Matt Dillon, which is included in DragonflyBSD 2.0
Now, give up your hesitations and subscribe to the tux3 mailing list. Always keep an eye on everything Dan does because he is really smart!
PS: Digg the story!