~650MH/s here, maybe 3kb/s being used on average.

ETA: Probably very relevant to note how many mining "threads" are active on the rig. 2, in my case, but Phoenix 2 dumps all the work in the same work queue.

ETA2: After reading TRL's post below -- noticed something was wrong with my numbers. Realized I'm running Skype + the BTC daemon which probably contributed to higher bandwidth use in my guesstimate (just looked at total bandwidth consumption on computer over 10 seconds or so). 140/24 = 2.333MB/hr, /60=.0388/min, /60=.00064814/second, *1000=.65KB/s -- Either way, it's probably insignificant consumption for most.