[quote name='gunm']They use UPS for Prime, which I believe many CAGs have. For me with FSSS, they will use USPS, which is 3-5 business days.[/quote]They use UPS for any standard/2-day/1-day shipping, which obviously would be anything with Prime.
They also use UPS for FSSS when it's something that wouldn't work via Media Mail, such as a Tivo, game console, or the like.
Anything that is media mail-shippable, such as books, movies, games, CD's, etc., that goes media mail for FSSS.
I've heard some people talk about FedEx being used for shipments recently, though I'm curious if that's for just one warehouse, or just in random cases. Everything they've sent me, save a TV purchase, is UPS or USPS.