Valve has, so far, added new achievements and unlockable weapons to three of the nine player classes in Team Fortress 2. You'll have to wait until 2009 for the fourth, though.

"Well, it won’t be this year,” Valve Vice Prez Doug Lombardi told Shacknews. “But we’re going to keep evolving TF2. Once Left 4 Dead wraps, you’ll hear us clamouring more about [the next TF2 update].”

Such a delay was hinted at back in September, when TF2 designer Robin Walker mentioned on the game's developer blog that much of the Team Fortress 2 team has been lending their multiplayer expertise to Left 4 Dead. Or so they claim, anyway. If you happen to see the TF2 team at a Washington strip club antagonizing dancers with a dollar bill on a string, go tell them to get back to work.