This coincides with my experience:
http://www.physics.usyd.edu.au/~cross/cricket.html - "1. Heavy vs Light Bats
The crowd loves a batter who can hit sixes. If you want to hit the ball as fast and far as possible, should you use a light or heavy bat? That's an age old question with plenty of answers, but which is the correct answer? Light bats can be swung faster than heavy bats, but only about 10% faster (for the usual range of bat weights). Imagine hypothetically that the bat weighs 10 grams - light as a feather. If you swing it as fast as possible, you might get the tip to travel at say 160 km/hr. Now double the weight to 20 gm. This time the tip travels at about 159 km/hr. The problem here is that your arms weigh about 8 kg all up, so the extra 0.01 kg is hardly noticeable. Most of the effort needed to swing a bat goes into swinging the arms. That's why light bats can be swung only about 10% faster than heavy bats.
If a light bat was swung at the same speed as a heavy bat and both hit the same ball, the heavy bat would pack more power since it has more energy and more momentum. But light bats can be swung 10% faster. If a bat is swung 10% faster, the ball comes off the bat about 7.5% faster. That almost makes up for the fact that light bats are basically less powerful when swung at the same speed as heavy bats. The end result is that heavy bats are about 1% more powerful than light bats. Having a heavy bat is a definite advantage if you swing all bats at the same medium speed, but if you need to move the bat quickly into position to strike the ball, a light bat will get there faster. Heavy for a 10 year old might be light for a 100 kg cricketer, so the real answer for raw bat power is to use a bat that is as heavy as feels comfortable to swing."
The consequence for me is that I own a lovely bat that I find, for all practical purposes, impossible to use. I'm considering having some weight taken off it. Also I've also noticed that recently bought bats have tended to put on weight. My theory is that they're kiln dried to improve their weight:size ratio but take on ambient moisture and settle at their authentic weight. I've noticed an increase of about 2 oz. Anyone else found this?