What I ended up with is Crashplan a peer-to-peer backup application or, as I like to call it, buddy backup. Crashplan runs on Windows, OS X, and Linux systems, and all you have to do is install the software -- did I mention the basic version is free? -- and have it invite your friends to back up their data to your computer.
Code42, Crashplan's creators, run a connection broker so multiple computers behind routers and firewalls can backup to each other and, for those that don't have friends to backup to, run an online storage service you can direct your backups to. Crashplan dedupes, encrypts, and compresses data to both local (USB or NAS, take that TimeMachine) and remote destinations, and the $60-plus-per-computer version does CDP and multiple versions. Best of all, when three days go by without a backup I get an email.
I set up an old laptop with CentOS and a USB hard drive for my friends to back up to. Their data is stored in cryptic folders on the USB drive, so I have no idea what they're backing up except that it is less than the quota I assigned each of them. When a friend's teenager lost his laptop, we recovered all his data to the new one across the LAN in my apartment, which was much faster than any online service could have been.
Cucku backup has a similar feature set built as a Skype plug-in, and so it uses Skype as it's data transport and connection broker. Cucku's biggest limitation is that it only supports one backup destination across the Skype Net for each PC, and each PC can only back up one other. Might be good for some, but I needed to hold backups of my entire support group.
Code 42 also has a Pro version they're selling for backing up the sales force's or senior execs' laptops, which explains how they can give away such a useful tool.