Did anyone ever seriously use it? It never made much sense to me -- if you're trying to optimize for performance, S3 is already pretty good and a CDN can make that even better; if you're trying to optimize for cost, you wouldn't be using S3 in the first place.
1) Universal torrent support is prerequisite to broad adoption. Having S3 be part of that network is nice.
2) It gives a fallback to exploding costs if something I do goes viral. I have the option of a weekend hackathon.
... and so on.
It's one of those features I like even if I don't use.
(And no, that's not actually common of features -- most of AWS, I wouldn't mind if it was not there)