Basically, as Ars Technica says, this is what .Mac backup should have been. In fat you have to ask yourself why Apple, with access to the OS at a level no third party vendor could possible hope to match, and with .Mac integrated directly into the system preferences, didn't do this first?
Update: The bad news? It doesn't work, at least not for me. The Mac Mozy application hangs during configuration as it rummages around on my disk indexing all my Microsoft Powerpoint files. The response from customer support was less than helpful, which was surprising, I guess I've got used to really good customer support from all those small Web 2.0 start-up companies that are really interested in their product and how you interact with it...
After setup it just hangs trying to index things...
Update: Well, it sort of works. Somehow I managed to get it past the hang by mucking around deleting preference files and other stuff you really shouldn't have to do, and managed to do my first backup. Except I don't trust it, after running for a couple of days now its continually mis-reporting the number and size of the files its sending for backup. That doesn't give me a lot of confidence that my files would be there if I needed them. So in summary, looks good, but not quite there yet. Like the customer service, I guess those pesky Web 2.0 start up companies have left me wanting more from a 'beta'.