http://www.exrx.net/WeightTraining/Myths.html
Performing lighter weight with more repetitions (15-20 reps, 20-30 reps, or 20-50 reps) does not burn more fat or tone (simultaneous decrease of fat and increase muscle) better than a heaver weight with moderate repetitions (8-12 reps).

http://ast-ss.com/information/?p=935
Training with higher reps and lighter weights will not burn fat but it will reduce the stimulus for muscle growth.

http://www.bullz-eye.com/furci/2008/0404.htm
Very simply, performing 12 reps instead of six to eight per set will have no noticeable effect on the amount of fat you burn.

http://www.articlealley.com/article_809923_23.html
By modifying rep range to address muscle definition, the bodybuilder adversely impacts the overload experienced by muscle tissue, and will potentially begin to burn away a portion of muscle mass that was gained with lower reps and greater weight. Instead of improving definition, this particular weight lifting technique will contradict this very goal by harming muscle, as a larger number of reps per set have no more of a positive impact on muscle definition than low rep workout plans, but they do reduce fatigue and overload, adversely impacting muscle gains, and risking the loss of muscle mass when following a lower calorie eating strategy for fat reduction.

http://www.wannabebig.com/training/bodybuilding/five-of-the-top-bodybuilding-myths-exploded/
First off, a set done with twenty reps will burn only marginally more kcals than a set performed with five reps. If you wish to lose bodyfat then you should do so via diet and aerobic exercise