This might be very related, actually - Dropbox just sent out an email announcing downtime for a move to a different data center.

Upload is probably much less than half of dropbox's bandwidth. If multiple users have the same file, it only needs to be uploaded once; but it needs to be downloaded every time someone syncs a directory containing it to a new machine.

Also, backup solutions based on S3. Most of their traffic is inbound.

About 90% of Tarsnap's bandwidth is inbound... but most of Tarsnap's AWS costs are for storage, not bandwidth. Backup services tend to store a lot of cold data.

As a Tarsnap customer, would this allow you to stop charging on sending data to Tarsnap, or does that still cost you somewhere in the lineup?

Tarsnap's upload costs cover the actual bandwith costs, the per-operation cost of S3 PUTs, the SimpleDB operations for checking account balances, some data storage (when you delete data, you stop paying for it; but I pay until the garbage collection job reaps those blocks)... there are lots of costs. The bandwidth was a significant part of it, though.

I need to crunch some numbers and see how the economics work out before I can commit to anything, but I'm certainly looking at adjusting the pricing.

I assumed there was more to it than just bandwidth costs, just wanted to get an official answer. Thanks.