I found
this review by Penny-Arcade to be quite amusing. Especially the part about the mic system:
"I was glad to see that the PC version lets you select between Push To Talk and Open Channel for voice, because it's not really a Push To Talk experience. If Donkey Konga is a game that is, at root, about "Clapping With Your Friends," Left 4 Dead is very much about "Saying Oh Shit In A Very Loud Voice." When a torrent of ravenous dead are running down on you, there's no opportunity to extend a pinky and daintily initiate conversation re: your collapsing skull."
I changed mine just now (Options > Audio > Voice Communication Style > Open Microphone) so I can remove one annoying button press in that game. Now to remember to mute my microphone when I'm yelling at my cat / computer / talking to Sara...
Anyway it should be a lot more immersive if people are having conversations in the game instead of reaching for the damn C (by default) or V (default for
TF2, which I changed mine to) button all the time.