Slush - what's the word on service? Are you considering any kind of SiteBacker DNS load balancing to help with traffic distribution between colos - that's helped some of my environments with DDoS.
DNS load balancing does not help DDoS prevention, unfortunately. There is not real way how to prevent DDoS when attacker uses 1.5 GB/s of traffic and tries to open 2.2 million connections per second from various IPs, like last attack on Sunday.