The BETA has launched and Blizzard is currently testing it's servers to make sure their new platform is running smoothly. Blizzard always takes a little longer to launch their titles and given that they really want to nail their new BattleNet platform, I'd say the BETA will be tested for a good 4-6 months as they fix/patch bugs with the live community. After that, I'd give them another 6-12 months to do final touch-ups.
You can't get the BETA. You have to be invited by Blizzard through battle.net.
Also, the current OFFICAL time frame is the first quarter of 2012.
Gamestop claims March 3rd.
I'd love to be wrong (and you right) but Sellers have claimed many dates with D3...which always got postponed. Blizzard release games "When they're ready"...which I believe will be by Blizzards standard in about a year or so...
That said, from a marketing perspective, D3 will be released on Q1 (regardless of the year).