HOW WELL DOES IT WORK?

It gets phenomenal results! To give you some examples, America's Most Versatile Border Collie for 1999 is clicker-trained. The 1999 Australian Police Dog of the Year is clicker-trained. And right here in South Africa, the holder of the World Record for Speed Weave Poles is clicker-trained.
One trainer has said that clicker training is faster and more reliable than conventional "J&P" (jerk & praise) training, but that it demands more from the trainer. This is probably true, but it's a lot more fun for you as well as the dog! It also teaches you the skills you need to be a successful handler - patience, consistency, good timing, and you can use these skills in other areas of your life as well. (In fact, Karen Pryor, who is a marine biologist and dolphin trainer and who is usually credited with having started the whole clicker movement, points out that dolphin trainers all have unusally nice children!)