Those of you who pre-ordered Left 4 Dead 2
(for PC on Steam or at participating retailers) now have exclusive access to the momentous event they said would never happen. For the first time in history, two separate Valve universes collide. That's right: it's a Left 4 Dead
crossover! This is not
fan fiction! This is not
a dream sequence! The characters from Team Fortress 2 will
team-up with Bill's hat from Left 4 Dead 1!
Read the full blog post[l4d.com]