The Epsilon Program is a religious cult (and Scientology spoof) based in San Andreas that R* also used to tease GTA: San Andreas. It was referenced a bunch in-game by characters and on the radio. I believe some of what's on the site is from the 2004 campaign for San Andreas, but I'm not totally sure. The Twitter account is certainly brand new and starting to build up followers already. Some pretty funny stuff on the site, though.
Even though it's not technically new info on the game, I'm excited just because of the absolute drought of info after that initial trailer (and the two screenshots I suppose). Hopefully this means something is brewing.