No, I hadn't.
Those sound exactly like the journal mechanism I so wishfully imagined. Definitely on my MUST-HAVE list should I ever succumb to setting up a RAID again.

Oh, and I notice that someone at OLS this year will be discussing making RAID rebuilds more intelligent by using the filesystem metadata to only sync actual allocated data areas, rather than blindly syncing all sectors.

With a setup that does both of those, RAIDs would be much less painful.