Velogirl posted a great, great trick on how to teach yourself recently. She noted it takes "commitment", i.e. you have to sit straight, not hover over the bars.

She suggested starting by taking one hand off and putting it on your thigh, then the other hand, on your thigh as well. Moving the arms around etc. takes a lot more time, practice, effort, etc. But thanks to that trick I'm now consistently able to sit with no hands for up to a minute (under perfect conditions). I wouldn't do it going down a steep hill in traffic (seen downtown Vancouver), and I can't do it to perform some action yet because the movement makes me loose my balance, but I might get there.

I figure out it's a core-strength exercise.