EXRX.net is a wealth of resources for working out. The best section is their training myths area. For example their run down on why high reps don’t burn more fat is extremely detailed:

For the average fit person, it requires 20 to 30 minutes of continuous aerobic activity with large muscle groups (eg. Gluteus Maximus and Quadriceps) to burn even 50% fat; fat requires oxygen to burn. Performing a few extra repetitions on a weight training exercise is not significant enough to burn extra fat and may in effect burn less fat. If intensity is compromised, less fat may be burned when light weight is used with high repetitions.

For this and much more information, check out EXRX.net.

Thanks to Diana Rowland for link