[quote name='ITDEFX']
I wonder how much data gets transmitted on multiplayer games?[/QUOTE]
I can tell you about how much data goes through my modem under a day of heavy use (at least for me).
I've got the modem running through a router, to which two desktops and a Xbox 360 connects via ethernet. I also have another desktop, laptop, Xbox 360, and PS3 connecting wirelessly to it as well (the router supports my entire family's internet access). In general there's usually at least one PC and one Xbox running at any given time. Every once in a while we have everything running at once.
The last time we had pretty much everything using the connection at once while I was downloading files from various servers/clients I broke the 15GB mark for one day according to the tool I used at work to check modem data activity. A good 10GB of that was from my downloading activities, leaving about 5GB to normal internet/gaming activities between three computers, a laptop, and two 360's. Again, the internet use that day was heavier than normal.
Generally the entire stream of data through my modem on a more normal day is around the 2GB mark, assuming what I saw at work is indeed accurate.