Bad things! rsync isn't smart enough (AFAIK) to know that files have been renamed or moved: it just sees files disappearing on one side and appearing on the other side, so the daily delta can get big.
DRBD may be a good solution to this problem, although I haven't spent the time to see what it would take to replicate over ssh, and the kind of traffic that is incurred vs changes in origin.
I'm looking into using the incremental diff/snapshot feature of btrfs to implement a more efficient solution :P