Interesting points pclissold and berzerke, it sounds like there needs to be a way for the ISP of a targeted site to send a warning signal to the ISPs of the source sites to tell them to shut down those DDOS people at the source.

Thats what the abuse@domain.com emails are for i.e. abuse@linode.com

The problem with that is that I've found that sometimes the owner of the net block are the abusers. That's when I add their whole net block to my iptables ban list.

Well thats part of life, some ISPs just don't give a crap. It's rare I email an abuse@ normally only if someone's up to something major or I know the ISP is reputable (i.e. if I saw a linode up to no good)