We never shut down our clients when they go over bandwidth, but would like to to keep it somewhat under control.
We don't send automated bandwidth notifications, and sadly, it is not possible to have these messages sent only to the administrator.
At this moment, we occasionaly check the bandwidth page in WHM and see how things are going. What I am really missing here, is the ability to check the account history. For example: when I see a client that is 600% over bandwidth, I don't make a problem of it, but would like to see if this is just a peak or something that is developing since the past 6 months.
An ideal solution to this would be to incorporate an extra feature in WHM, accessable through the bandwidth usage screen which shows a bandwidth graph per month for one specific account.