Many thanks to ghost16825 for pointing me towards this excellent InfoWorld article: The great intrusion prevention debate. The article pits Sourcefire founder Marty Roesch against TippingPoint Chief Technology and Strategy Officer Marc Willebeek-LeMair. Folks, this one is not pretty. Marty demolishes Dr. Willebeek-LeMair by correctly arguing that IPS (called layer 7 firewalls by the Blog and elsewhere) is "a step in the right direction, but... the infrastructure itself can be orchestrated effectively to provide a much broader capability than just point defense in the face of a pervasive threat." Dr. Willebeek-LeMair's main defense: "To be as polite and as succinct as possible: You are simply misinformed."
This debate shows how a hardware vendor with a fast packet processing systems thinks he can change the world. Dr. Willebeek-LeMair's market-speak falls flat when critiqued by an actual security expert (Marty).
I highly recommend reading the entire interview. Some of you may remember the promises made by firewall vendors and see that the IPS claims are eerily similar. While I agree with Dr. Willebeek-LeMair's assertion that "IPSes will be integrated within switch and router elements" (it's happening now), the IPS is not a panacea.