I've been using Mozy for a few weeks now, and I'm a big fan. I like its backup method. You specify X CPU usage and Y amount of time, and it will wait Y minutes after dropping below X to do its backup, which takes a bit of CPU for the encoding process. That way it both waits until you're done with any intensive tasks, and it backs up just after you've done work that you probably want backed up.
If you wouldn't mind terribly, if you're going to sign up for Mozy, could you follow
this link? It'll give both you and I 256MB extra space on the free account. If you're already there, you can do the same thing by entering "QB67E8" in the code box when setting up your account.
I keep a free account just to keep my household costs down. I use it to back up important files that aren't media, which fits nicely into the 2GB allotment.
*edit*
Oh, and the other option out there is
Carbonite. I can't tell you anything about them, though, because they don't have a free account. They are $10 cheaper per year, though.