Guy, Retrospect backs up incrementally and lets you go back to any session—sounds like Silver Keeper is simply cloning. With your scenerio a 100GB firewire drive would hold 2 to 3 months of sessions and you would have access to all the increments. I use 3 firewire drives and rotate them off site daily and then archive the finished project to DVD. There have been many times where I've gone back a week to pickup an earlier version of a file.

Rob