I am always pushing backup - and some of you still aren't offering it. If you don't want to resell Intronis or Mozy or whoever, here's a little open source help to DIY.
From Google sites, "Bonkey is a simple to use backup system. It can backup to most storage devices, but it is specifically designed to be used with cloud storage solutions like Amazon S3 and Rackspace CloudFiles, which provides cheap online storage. You choose which files need to be backed up, select how often, set the destination and voila! your files are backed up. It runs on Windows and Mac OSX."
Sourceforge has more: "An easy to use application for backing up files to multiple locations, including Amazon's S3. Runs on Windows, OS X and Linux. Bonkey is based on the Eclipse RCP and requires Java. Downloads at thebackupmonkey.blogspot.com."