I haven't heard of DropBox, but Mozy saved my butt last week. TWO of my computers suffered from "catastrophic system failures" within three days of each other. Mozy used to be free up to 2gb, but I don't think it is anymore. Anyway, I set Mozy (which runs in the background) to back up the folders of my choosing every 15 minutes. I'm insanely glad I did it.