We look forward to Xbox Live Game With Fame announcements, largely because of our lifelong dream to play Madballs in Bebo Invasion with U.S. Secretary of Agriculture Tom Vilsack (someday!). There's even more reason to pay attention to the most recent one, as it claims fans will get a chance to play new Left 4 Dead DLC "Crash Course" on September 23rd. The power of deduction indicates that the DLC should be released on or before then, assuming it's not part of a special sneak preview.
Oh, and in case you're curious, those selected for Game with Fame will be playing against the band Paramore. Left 4 Dead is probably the best thing they've played in some time.