I've been using both desktop and on-line backup for my laptop for a while. One thing I learned from the tech fallout after Hurricane Katrina is that "off-site" backup isn't necessarily far enough off-site; many small business people who followed the rule of taking a copy of their files home with them got flooded out of both home and office. So I've played with a couple of different off-site, background backup services. I was using Carbonite for a while, but it doesn't back up open files and it excludes files it regards as system files. So I switched--now I'm using Mozy. It backs up open files, including my Outlook.pst file and archive files. 2GB free, or unlimited for $4.95/month. Encrypted files, will use a public key, has a Mac client too.

One tip if you decide to try it: it takes *forever* to back up a pst file. However, once you survive the first backup, leave mozy running and set to automatic backup, and it will only need to transfer the delta (changed blocks of bytes) rather than re-encrypting and re-uploading the whole thing. Unobtrusive and easy. Enjoy!