Lastly if an ISP is going to make a cap on their network, then THEY should provide you with a way to monitor the account via a web portal or at the modem itself, thats like having a bank account and not being able to check the balance. Expecting 3rd party vendors that have nothing to do with the ISP to handle this for you is kinda silly. If the ISP can see your monthly download, then they need to make that available to you. Not doing so and busting you for it seems like entrapment to me.
Lycan, I totally agree w/ you that they shouldn't cap you, and if they do, should at least provide you with the means to monitor your usage. Unfortunately, I haven't heard of one ISP, nor have I ever had one, which provides this. Additionally, many ISPS won't even tell you what the maximum upload/download amount is, just that you went over it. Therefore, it would be extremely nice to have this feature.
I don't see it being that hard to implement. Currently, I am using 'BitMeter' which is a great little tool that tells you your statistics daily/monthly, even by the hour. The problem is, when I have my roomates coming in during the fall, I'm sure they are not going to want to install this and send me their stats every day, along w/ everyone else in the house. So, I'm sure you can understand the desire for this feature.