I'd place another vote for SpiderOak. The fact that you can pool storage between computers on a consumer plan is great, and their DIY API looks promising.
http://macsoftwarespotlight.com/ is offering 35% off SpiderOak pricing (less than an hour left). their DIY API seems simple enough and hacker-friendly, although i hope they standardize their API so it's easier to migrate from, say S3.
I've been pretty happy with SpiderOak but I haven't needed to use it to recover files yet -- I feel that the interface may be a little too cumbersome than it should be.