A good book with more of a scientific bent is Michael Kelly's Death Touch. He demystifies the pressure points by correlating them with medical science (He's an osteopathic physician)
To respond to some of the statments, it is my opinion that if you want to study pressure points to create pain or influence acupuncture points you need to study how the reverse the effects or the healing aspects somewhat as well. Kelly points out that you can cause a vasovagal reflex and drop one's blood pressure-this could be a serious health risk.
My research in the topic and a survey conducted for an indepth treatment of the topic suggests to me that pressure point usage (kyusho jitsu) is applicable in aikido in the application of atemi-waza. However, I don't foresee the "knock-outs and death touch" elements being of interest to or very useful for aikidoka to use on a regular basis-plus they are dangerous. I do believe that the pain compliance aspect is quite effective in helping set up a technique by dropping a shoulder or positioning uke for a throw. It also has use for controlling ukes with locking and pinning techniques. If I ever get the time to finish it I hope to publish and aikido version showing how to integrate pressure point manipulation/strikes into aikido technique without losing the flow.
Just some thoughts. This has been a long-standing interest of mine since it is my belief that the transition from art to street is in the use of atemi-waza and kyusho jitsu.
Dr. John Riggs