I was a masochist and hand-rolled incremental tar snapshots to Glacier using a cronjob. It works great for keeping price down, though I learnt the "lots of retrievals" lesson the hard way once I actually tried to retrieve my data. I now compromise by doing a full snapshot monthly and incremental daily, so I'm upper bound to 30 retrievals.

I'd highly recommend not repeating my mistake - use a real backup service for your actual data. Though rolling your own can be fun and interesting, it's probably a bad idea to bet your data on it.