I have witnessed two bows that over a 5000 shot period drop poundage from 70lbs to 67lbs. Then after 2000 more shots or so, drop to 65lbs.

But more importantly than limbs loosing thier spring, was the cams started getting a whole lot of slop in them. I had to compensate by getting larger axles and I would get a friend to take off a few mils to get a decent fit.