I've got Terabytes of data that need to be archived and possibly recalled later (trading logs and market data preserved in case of an audit). I'm not at the scale of Glacier. If TarSnap had a readonly vault (files in said vault would never change) then it would be able to distinguish the files and split between the Glacier and S3 offerings.
Drop a note to http://www.haystacksoftware.com/arq/ - I'll wager they will have an option to create "Glaciered Archives" of folders within a few months. The developer there has already expressed some interest, and suggested that Arq would lend itself to pointing at a folder and storing it off to a Glacier Archive (with all the caveats around 4 Hour delay, 24 Hour of Availability, Costs associated with restores, etc...)
That's awesome news. Just being able to take a folder on my Drive, and say, "Archive this 5 Gigabytes of photos for the next 50 years" - and know it will cost me around $30 (and, as time goes on, likely less as the storage drops) and I won't have to worry (much) about it, will be a big win - even if you don't come up with an easy way of integrating with the normal S3 backups - I bet a lot of people will love that feature.
