Valve's new patch for Left 4 Dead is a biggie that primarily fixes exploits, but there are some great additions to both the single and multiplayer games, too.
For the Survivors, it's mostly fixes, but you now can't scale the buildings using Infected routes or leap onto ladders after being punched by a tank. The Infected, on the other hand, get goodies galore.
The Hunter now pounces hard, and can get past melee a lot more easily. The Smoker's tongue has had a lot of fixes so that he's now deadlier, faster and more accurate. The Tank appears more often, nearer to the players, but can't fraternize with the Witch so much. He's also far more resilient against shotgun blasts.
Even the Witch gets some loving, with the chance of her appearing increased and appearing with the same chance on both sides of the Versus race. The Boomer, however, will just have make do with his boosted Infected-in-Arms.
Overall though, loading times are up, the HUD is clearer and people can't chop and change teams willy-nilly.
The PC patch is already waiting on Steam for download, and the 360 patch will be coming over the next few weeks.
One thing that the patch doesn't change: Francis still hates vans.