I know that there's been many wheelie post on the forums, as I've read most of them. I'm a pretty decent rider who's been trying to ride wheelies for some time and was convinced that they were just very very very hard. Determined to learn, I searched for something I was missing and I found it. This has been mentioned many times, but I don't think it was emphasised enough.
If you can pull the bike over backwards if you want, and if you can take a coulple pedals and hold the front end up under power, then you are ready for the tip. Here it is, the secret to riding wheelies:
Ever since you learned to ride a bike you have intuitively reacted at the first sign of a bike tipping. If a bike begins to tip to the left you insticitvely steer left to bring the bike back under you and straighten it out. However, when you try to wheelie, if you steer into the lean the bike will go over even faster. What you have to do is learn to steer against the lean. As the bike starts to lean just steer in the opposite direction. It won't feel right, and you'll have to think about it at first, but it works.
Like I said, I tried and tried to wheelie, but never felt like I had any control at all. After about half an hour practicing this technique I was wobbling my way down the road. I still need lots of practice, but for the first time ever I can control the bike and it's just a matter time to get better.