Hmmm, on Xbox 360, I occassionally get a "What's UP!" At the beginning of matches. Maybe say a compliment or 2 if people are playing exceptionally well (it happens!), and always try to leave with a "Good game!" to the better players.
Voice Chat shouldn't affect Xbox 360 match connection speed much, if at all, though, should it? I'd figure the 360 always has a channel / partition of your bandwidth reserved for voice chat, shouldn't it? I always figured that's why FPS and such don't run as smooth online on 360, because their network is attempting to optimize for the Gameplay / Voice chat together, where as PC's just have the internet open for general use, so their bottleneck is decided moreso on a software-to-software basis. Any network people around here able to tell me if my theory is correct or not?
I always mute my mic though, when I'm not saying anything important... breathing/talking to others in room/random background crap does NOT need to be aired over the internet! I wish more people shared that sentiment....