I don't think it works that way... I understand it as follows:
Let's say that there are 10 users on 3Gb caps. The TOTAL allotment of bandwidth to all of them is 30Gb. Every user is entitled to their 3Gb and you can exceed your cap as long as the total use by all 10 users is less than 30Gb.
So, let's say that user A reaches his cap first while 8 users (B) have only used 1Gb and 1 user (C) has used 500Mb . The total usage is then 11.5Gb, leaving 18.5Gb available in the pool.
Repeat. User A then does another 3Gb while all the B's do another 1Gb and C another 500Mb. Total used is now 23Gb, which still leaves 7Gb in the pool.
Repeat once more. User A does another 3Gb. The B's do another 1Gb. C does another 500Mb. The total use is 34.5Gb. User A is then capped at 9Gb, the B's are capped at 3Gb and user C still has another 1.5Gb to go before he gets capped.
Make sense? Yeah, not really. It means the alleged 'abusers' of bandwidth will just have to get in early while there's still bandwidth in the pool. I honestly don't see how this will change anything.
Juice