Rate limiting UDP,Multicast,ICMP

A little more information. We sell 100Mb Ethernet pipes to the Internet. (Yes, there are a few of us left). A fair number of these customers are small businesses. Usually, they have servers but very little IT support and even less IT know how. My thought is to rate limit UDP and ICMP at the customer port to no more than 3Mb/s so WHEN (not if) a customer is compromised, the effects are somewhat limited and my MAN pipes have some measure protection. The question is, what am I not thinking of? DNS, TFTP and such should all operate virtually unaffected, as they are not bandwidth hungry services. Thomas