As a theoretical case (but not totally impossible), if you leave your 40Mbit/s connection going on (read downloading/uploading) at all times, you gonna eat up 250GB in ~14 hours not 1 month. For all they care you could upload/download everything and the kitchen sink off Crashplan or whatever. Those caps are insane.
As for filesharing... If you have to UL 136GB to get 980 GB for file sharing you don't know what you're doing. Stop torrenting that's not the best source. As an aside does it say anywhere in the contract you cannot do filesharing?? Or that you can do only certain things with the internet connection you pay for? Are they outlined all those things from 1 to 1 million?
Do they really wanna have a guessing game and try to prove it that you do I don't know what traffic if, say, you put an encrypted VPN on top of everything?
Otherwise, yeah, certain routers do have traffic meters, including notification blinking lights and shutting the connection down entirely when it reaches a limit. My Netgear N900 has these (and I stumble on them by mistake, never in my mind have have I thought to turn on something like that).
Hopefully Google and their fiber are gonna eat all these providers up
. Has anybody considered moving to Kansas City, MO?