From Steam News:
Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:
Encore mutation: Taannkk!
Dead Center – The Mall
Survivors can no longer bypass the storefront mini-finale.
Dark Carnival – The Barns
Survivors can no longer bypass the barn interiors.
The Parish – The Waterfront
Removed the Survivor zombie-jump exploit in the first alley.
The Parish – The Quarter
Survivors prevented from using short cut over the top of the fence.
Various bug and exploit fixes for the first 3 maps.
Added survivor respawn closets – some temporary while we work on the maps.
Added navigational aids to maps.
Changed the first map’s ending as an experiment – please give feedback!
Added alternate route around boat mast – please give feedback.
To help with public testing, we fixed more bugs and exploits than we normally would on maps that are still in a transitional state. We are holding off on many changes to the finale right now as that map will change the most.
As you can see valve is trying to prevent map exploits as much as we are. Lets hope they don’t close all the holes. We still need some for Rochell and Coach.