I know that I have never come close to reaching my bandwidth limit, and that includes downloading things like Linux Mandrake (1.6Gb) and ELX (1.1Gb). I also do a lot of downloading on Morpheus, and surf about 6 hours a day on average.
The reason that they have the limit is so that someone doesn't hog more than their share of the bandwidth that is available (at least, that's what they told me).
I just found something else out too... my ISP no longer has a limit of one machine per account



They just want you to bypass the router when they are troubleshooting a connection problem.