I should add, when you're releasing the ball it's all in the fingers.  The momentum created by swinging the ball gets transfered to your fingers mainly.  this is why some people get so many revs on the ball and it looks effortlessly.  It's because in many ways it is.  they just have a nice swing and are able to transfer a lot of this energy to the fingers as they release the ball at just the right time to create maximum revs.  Make sure you're bowling with your fingers so to speak and follow through.

And regardless of what anyone says, in my experience the most revs you can generate and still control and repeat (this is the key as you can probably make more revs, but you wouldn't be as consistent and accurate with it) your shot, the better off you are.  Todays balls like revs and you should put as many on your ball as you can control.  This doesn't mean you need revs to be a good bowler, of course.  I've found revs give you a little more margin of error (even on a block, outside shots have more revs and come back and inside shots are a late release with fewer revs and stay on line...granted, I'm talking a few boards at the breakpoint here) and obviously create more backend and better carry.  However, the best shot is the one you can do over and over.