Mechwarrior Online never actually happened as planned (about a decade ago) but now it is a planned again: for 2012. We knew this was in the pipeline, but things seem to be shaping up, because the website that hails this fresh announcement is here, and it allows you to sign up and register your pilot name. I did that. You are not having my name. The FAQ is almost comedic in the range of things it addresses, failing to really address what the game is actually going to be like, but explain that long-ranged missiles will be "semi-guided", and the status of melee combat is undecided. It will, however, be a team-based multiplayer game. Also, bafflingly, it states: "MechWarrior® Online™ is running an offset timeline of the BattleTech® Universe. As of this writing it is 2011 and the year is 3048 within the game. In 2012, when the game is launched, it will be 3049." Okay then!
More details on PCG.