Syncplicity & KineticD
Data loss is a concern and in the past, I've lost files and regretted not being more systematic about backing up, plus now I also worry about losing my photos. The idea of off-site back-up appeals to me in case of a local disaster (house fire, tornado, flood) and because it's automatic.
I've used Syncplicity for a few years and have been happy with it & haven't found it a big problem for bandwidth. But the service is subject to the Patriot Act, which as a Canadian, is less than thrilling, so I also started to use KineticD, a service that resides in Canada, for some files (had one client with privacy concerns with US-based back-up). I need to decide whether to continue with both--it does get expensive.
I also recently bought an iomega eGo portable hard drive that is easy to use as a constant, automatic back-up and storage. When I go out of town, I disconnect and store it away from my computer so that if there was a fire or theft, I'd still have all my data. I can also use it with my laptop if I'm away from my desktop or just want a change of venue.