After been 1 years and counting, today my bandwidth 80gb just exceed, and that's 26 days in this month and still have 2 more days before end of the month, i was kinda happy with the result, just i open back my forum and i having bandwidth exceed 🙂
It's all fun and games until someone loses a forum 😛 But yeah, if you start going over bandwidth, you need to quickly upgrade otherwise your members will get frustrated at the lack of site availability.
If your site isn't popular and your are going over 80GB of bandwidth, you should be worried, not happy. You could have thousands of spam links heading towards your site, wasting your bandwidth, or a lot of hotlinking. You should look at where you are getting traffic from and any major inconsistencies should be taken seriously.