Just an FYI after speaking to a representative on chat.
Multiple streams: 2 max, don't have to be on the same network, presumably this includes mobile streams. In order to get more, have to sign up more than once, no way to buy "extra streams" like with Netflix.
Data usage: Unmetered on AT&T Internet (U-Verse & Mobile)
Recommended bandwidth per stream: 3 Mb/s recommended for HD (I'm guessing double for 2 streams). Channels are in HD.
DVR: No solid info for now. Can rewind within a channel (or watch past shows) up to 72 hours previous.
CC (Closed Captioning): Should work as expected.