In some ways this builds on the Podcast I had with keynote speaker, Ivan Krstić.
Blacklists were effective when we had relatively few threats but with the increasing sophistication, innovation, speed of time to market and effectiveness of bad stuff such as malware and botnets it has become practically impossible to blacklist everything.
Unfortunately this is only becoming worse and technology which has been just about able to cope is being left behind. You only have to look at my recent blog on why Anti-virus software may have to be relegated to a 2nd line of defence solution to fully understand the problem.
In addition if you listen to the podcast with Jose Nazario on how botnets have evolved you would understand why blacklists on the corporate firewall are also becoming ineffective.