I'm actually convinced it's a little sad that S3 becomes the defacto standard.
At its core, S3 is a key-value store and I don't think it's a very feature-full one at that. Indeed it has some very good features but I'm afraid people simply implement its API rather than spend time innovating.
Two things that I have in mind: - Retention delay - REST API (although both Swift and RiakCS implement that)
Otherwise, it's nice to see S3 becoming a web storage standard (or one standard emerging in general). Openstack Swift also supports it.