Just been having a play with this, and apart from a few no clip issues it works quite well, obviously 1st person is where it's at but I find it's still cool to be able to switch to 3rd person at any point with a press of a button. 
To get it working all you have to do is add the following bind to your Left 4 Dead CFG, which is located in :\STEAM\steamapps\common\left 4 dead\left4dead\cfg
bind "whatever key you want" "thirdpersonshoulder; cam_idealyaw -3"
Here's a pic of what my CFG looks like with the command inserted (as you can see, I binded mine to mouse button 5).
Note, you'll have to set the file as read only otherwise the bind will be overwritten when starting the game (right click CFG > properties > read only > apply).


Quick vid to give you an idea how it looks:
[/QUOTE]

To get it working all you have to do is add the following bind to your Left 4 Dead CFG, which is located in :\STEAM\steamapps\common\left 4 dead\left4dead\cfg
bind "whatever key you want" "thirdpersonshoulder; cam_idealyaw -3"
Here's a pic of what my CFG looks like with the command inserted (as you can see, I binded mine to mouse button 5).
Note, you'll have to set the file as read only otherwise the bind will be overwritten when starting the game (right click CFG > properties > read only > apply).


Quick vid to give you an idea how it looks:
[/QUOTE]