I figure I'll make another comment to point out the fact that communication is only as useful as three key factors; the speaker, the listener and the medium.
Problems with the speaker tend to revolve around trying to convey information whilst being totally unable to present a context. For example, I can play Resistance 2 with my friends and announce "sniper on the clocktower!" and they'll understand. However, you might not. The reason you might not is because you cannot actually ENTER the clocktower I am referring to, and what I mean is "sniper on the building in front of the clocktower." That's a few seconds of confusion that'll probably get you shot.
The reason this problem persists is inability to universally convey information. I cannot sit down with players pre-game and say "Okay, HERE is the Bunker. HERE is Sniper Alley. HERE is the Crow's Nest." I am forced to try to use overly-accurate descriptions to get information across. This brings me to point two...
The Listener. Sometimes, people are just retarded. Occasionally they use an excuse like "I not speak English", but when I've listened to an hour of twat-talk in what passes for English in the inbred little backwater my teammate hails from, I don't bite.
Here's a hypothetical - a game where there are two teams, a Red and a Blue. Both teams have a Building they can use for sniping plonked right next to their spawn point. The buildings are even colour-coded for simplicity. There are gamers out there who, if you yell "Sniper on Red Building!" they will stop dead and ask what the fuck you are on about. Then they will get shot by the guy you were trying to warn them about, and spend half an hour bitching that A) the guy came out of nowhere, and B) his team are a load of fags for not helping him.
In other words, communication with a cuntbag is a waste of effort.
Finally, the medium. Unless the games are region-locked, there is a chance that the reason the other guy is ignoring everything you say is you are saying it in German, and he's listening in French. I seem to wind up in games with a lot of French / Spanish / Italian gamers, which can make organisation a *****.
In short, in order for this to REALLY work, Valve need to do three things:
1) Region-lock games so everyone speaks the same language.
2) Instigate a system where players can, as a group, study the map and learn how to convey information quickly and accurately together BEFORE the game is launched.
3) Make the dipshits go back to Call of Duty, or wherever the fuck they came from.
Conclusion - not happening.