I have to agree with Jimboden.. within about a 30mb.. my usage is pretty accurate.
At .7g on medium.. with say 2 hours a day usage.. you are looking at about 45g a month used up just for netflix.
MOST people i know.. stream on higher than medium to get the picture quality.. (i beleive, a new account DEFAULTS you to high as well, so if a user is not aware and doesnt go in and change it)
On high, you are looking at up to 3g / hour. same 2 hours a day... thats up to 6g a day... 180 a month!
Let alone, if you are running software (win8 netflix app) or a device which supports SUPER-HD.. you can use up to 5g a hour.