~4 years ago I wrote a script which will sync my drupal files directory between two servers [ I used rsync for that ], the problem with rsync was that it fetches a checsum of every file and direcroty over SSH which was very slow, and the critical issue was I have no history of the data - and if I am maintaining multipule syncs whats the point in rsync.
I looked @ svn at the time which was extreemly slow with binaries [ zip, tars etc ], Git and the git protocol in specific did the full sync [ ~1GB ] in under 45 minuets - over the Internet which was quite good IMO.
Well, Finally drupal 7 is released with a lot of promising features - see full list 
On the 15th of December 2009