Personally I like google docs for my document backups. Despite the fact when you use it your documents are essentially converted to html (word) and some form of database representation (xls) when you use it. IE not a true backup. But the contents there which matters.

It doesn't do files however, and there is no 'sync' system yet. :(

But automatic backups are very nice. I don't have any going myself. :(

With dropbox I was going to install it, however the Linux client was designed specifically for gnome and no hint of KDE or 'generic' support yet. (It could have used fuse which would have made it good!)