I was looking through my flagged articles in NewsFire, and I saw this post mentioned that Quicken 2006 has support for backing up the data file to .Mac. Since I just installed Quicken 2006, I enabled this feature.
The first time that your data file is backed up, it asks for a password. Then what it does is it creates an encrypted disk image with that password, and copies the data file into it. Then it copies the disk image to your iDisk.
This is pretty cool, as you get the automatic off-site backup, as well as the security of the encryption built into the disk image format.