EXCELLENT - How about Rated 5 out of 5 stars
This sounds like a perfect idea. I've already received 2 phone calls from my ISP letting me know that I've either exceeded or am coming close to exceeding my Bandwidth. I wish that this supported (US) ISP's popular over here: COMCAST, and TimeWarner. Both of these have recently publicly (legal issues) promised to maintain bandwidth quotas.
Should be soon for Comcast
About Comcast, I replied to you by email, but just to let other users know, Comcast will soon implement a viewable online usage meter starting January 5.
So, as soon as any user sends me the infos (see http://extensions.geckozone.org/Minimeter-en#askmodules), I'll add the module.