Arq is a great little Mac OS X application for backing up your personal data to Amazon S3. It provides transparent, automatic, incremental, encrypted backup to S3 using a solid application with fine control over inclusion/exclusion criteria and nice little bonuses like S3 budget and network throughput preferences.

The developer definitely seems to have the right idea: he "stole" the design for a content-addressable storage system from Git and provides an open source restore tool called arq_restore to assuage any doubts you might have about vendor lock-in (the Arq S3 data format is publicly documented).