As a forced Comcast user, out of curiosity, I checked my usage. It's day 5 of the month and I've used 70GB so far...previous months I've downloaded anywhere between 260 - 290 GB of data.
I work from home and access all my work data over my internet connection (I move very few files around - it's mostly rdp/ssh sessions, git interactions), use voip phones (both work and home), my kids almost exclusively watch "tv" via Netflix and YouTube and I would say my wife and I maybe watch 4-5 hours of streaming tv a week. Apart from that our internet usage isn't anything out of the ordinary and we're still exceeding the cap.
Comcast is insane if they think classifying anyone over 250GB of consumption a bandwidth hog especially as streaming services continue to grow in popularity - and eat into cable revenues.
If I had any real choice of provider, I'd be switching away from Comcast in a heartbeat.