New research suggests lighter loads can be just as effective, but with lower risk of injury than heavy loads.
Personally, my experience agrees with the results of the study. I find that the secret to building muscle is to lift on a regular basis. The amount of weight doesn't matter so much.
BLX Blade 98. 13.58 oz., 12.55", 366 SW. 16x20 (outer mains skipped)
Pre-Stretched Ashaway Kevlar 18g/ZX Monogut Natural 16g, 66/46 lbs