Orange Box have experienced lag while playing 8-on-8 or 6-on6 Team Fortress 2 games, and they've reacted quickly, making a title update for the game designed to fix the issues.
Now, the title update must make it through the gauntlet of Microsoft's certification process. Should it make it out alive, 1UP says you can probably expect the lag situation to be improved by this weekend or early next week. Good luck, little title update. We're rooting for you.