Here in India, they dont terminate your contract. I have a 2 mbps (upto 30 gb per month) ADSL connection that will drop to 256 kbps after the 30 GB limit. i pay ~$25 USD for it. You can increase the limit by paying more :). Of course if you pay some extra again, you can get more @ 2mbps. they do make it very clear though when you sign up.

when i was in US (virginia) comcast was notorious for dropping speed after 60 gb usage and there was no fine print about it.