From the Left 4 Dead blog: "After months *cough*year*cough* of play testing not just the Cold Stream campaign on the PC but the entire DLC consisting of Blood Harvest, Crash Course, Cold Stream, Dead Air, and Death Toll, we are ready to release on the Xbox 360.
The date will be July 24th. There are some other surprises and details we will give you later but for now we just want to confirm an often requested feature. With the update going out at the same time (also for the PC), all of the mutations will be available at all times. This will allow players to choose to match into games playing Taannkk!, Gib Fest, or even a user created mutation like Confogl."
Finally we know when we will get to take a shot at (or shuffle through) the newest Left 4 Dead 2 map. The map doesn't follow the L4D or L4D2 canon, so don't expect any story tie-ins. This is strictly a place where zombies go to kill or be killed... again.