Thanks to Ronaldo Vasconcellos for pointing me towards What to ask when evaluating intrusion prevention systems. This is an interview with Bob Walder of the NSS Group. I agree with the conclusion of the article:
"I can't stress enough the need for a thorough bake-off in your own network. It's likely to be very different from a test lab environment and may throw up some very interesting challenges for the vendors."
I provided inputs to an IPS test done by a partner company. I would be happy to conduct thorough IDS, IPS, or firewall testing for your environment too! Send an email to richard at taosecurity dot com if you are interested.