I've been using SyncBack Pro in various scenarios for a while: http://www.2brightsparks.com/syncback/sbpro.html

It's extremely configurable, supports many source/destination options, and pretty cheap. It's not hosted, SAAS, or cloud-based. But, just point it to an S3 bucket and you've got the same thing.

One scenario I have is a daily snapshot of files, copied locally to a YYYY-MM-DD folder, then zipped, and uploaded to an S3 bucket. Another scenario is twice daily rsync-style backup that copies changes on a large directory to a backup location.