I was asking about it the other day. I track bandwidth on every one of my machines and at the gateway. So I have a general idea (and a 220 Gig available margin of error on a heavy month). While its not terribly difficult, I probably don't have as much legacy equipment as Comcast. I know the hamster powering my local CMTS gets tired at rush hour.
I just do it at the gateway myself. I personally feel it is much more accurate when I'm tracking bandwidth that actually gets passed.
