Doesn't Dropbox run on S3? Or is that the company that recently moved off AWS into their own datacenters? If so that was a good case study. (I'm an all 5 certified AWS guy and while I love it, I like seeing the counterexamples to keep my Kool-Aid ingestion in check).
They used to. They migrated off of it because cloud is too expensive. 2 big components to that :
1) traffic to the rest of the internet from the cloud is "wtf" expensive compared to the alternatives. If you can do your own peering (like dropbox does), this goes double.
2) Actual disk storage is too expensive as well. It doesn't compare favorably with what you can get by building a blackblaze pod [1] (just an example).
3) Cloud does not match their usecase. They are write-heavy instead of read-heavy. So as the cloud optimizes for internet serving, it actually moves further away from their optimal price point.
There's an episode of software engineering radio that has a lot of details from the horse's mouth:
