Here in .au well its kind of like this. Every account has a limit but its much much lower then in the US. And you pay for above that limit. A large limit would be 25 gig or 50 gig per month (most people wouldn't have anywhere near that).

Thankfully, a lot of the good ISPs are making lots of content unmetered - specifically media stuff like tivo downloads and itunes etc (the stuff that would push the limits).