Click-L is the grandfather of all clicker training mailing lists. It was started in the mid-1990s by Kathleen Weaver, and has consistently been at the forefront of clicker lists since. Click-L has a new owner now, Kellie Snider, and its focus has evolved. Rather than being "just another general discussion list," the new Click-L focuses on the scientific side of clicker training. Kellie is the perfect leader for such a list. She's soon to have her Masters in Behavior Analysis from the University of North Texas, and her thesis concerns operant conditioning techiques for treating aggression in dogs.
Science and empirical evidence reign supreme on the new list. Currently, list members are debating the commonly-held rule of reinforcing after every click. One list member is even doing an experiment, complete with record keeping, to see what effect reinforcing after every other click has on her dog. Like many discussions on Click-L, members frequently pull out textbooks on Behavior Analysis or refer to research done on the subject. List members take no "rules" at face value here. They want proof--or at least evidence.
If you have any interest in the science behind clicker training, Click-L is a great list. I also recommend it for anyone who wants to become a better trainer. Although some of the threads can get quite detailed, the point of these discussions is not to nit-pick theory, but to identify the best, most effective techniques.