I learned how to powerload with a 21 foot jet sled. The interesting thing with these boats is that in order to steer, you must be applying power. The boat had a large profile with its top (think sail) and a relativly flat bottom so the minute you back off the throttle yopu would drift all over the place. It was very intimidating at first. You had to approach at a failrly fast speed to keep control. Pretty scary stuff when it is your dads brand new very expensive boat.
With my last boat, a 19 foot Seaswirl Spyder, I just had to get the keel between the bunks. One I had the keel in place, I could back off the power a bit. The boat would then center itself. I would then slowly apply power and she would slide into place. I would walk to the bow, lean over and clip on the winch line. The key as most people have mentioned is not too back the trailer in too deep. If it is too deep, your boat will not center properly. Also, make sure you trim your outdrive up. Your prop and skeg will thank you.
Once you get the hang of powerloading, you will never want to crank your boat on the trailer again. Just make sure it is allowed at your ramp. Some places don't allow it do to the errosion it can cause.
) so I have to stop when I hit the bunks. No power allowed to drive it up. I don't mind that part at all. I just don't want to have to make three passes to get on the bunks 
