Huh, and what's *really* cool about it is that they apparently export a userspace API for expressing IO write barriers. So with the featherstitch patch, you really can say things like "write these bytes to that file, and then rename it, but don't let the rename hit the disk until after the write has completed", except with arbitrarily complex dependency structures (!).
I don't really care whether I'm using soft-updates or journalling, just so long as my disk is safe and things are reasonably fast, but real write barriers could totally change the performance profile of higher level apps. (Except for ACID databases, of course; I guess that's why historically no-one has cared about write barriers, because the only important high-level storage service was ACID databases.)