I also highly recommend John S. Denker's "See How It Flies" (http://www.av8n.com/how/), which along with more "aviating" tips has a good discussion about circulation, the Kutta condition and the Kutta-Zhukovsky theorem. The Wikipedia page on the Kutta condition (http://en.wikipedia.org/wiki/Kutta_condition) is also quite informative.

I especially like this part from See How It Flies:

  We have seen that several physical principles are involved in producing lift.
  Each of the following statements is correct as far as it goes:

  * The wing produces lift “because” it is flying at an angle of attack.
  * The wing produces lift “because” of circulation.
  * The wing produces lift “because” of Bernoulli’s principle.
  * The wing produces lift “because” of Newton’s law of action and reaction.

  ... Do we get a little bit of lift because of Bernoulli, and a little bit more
  because of Newton? No, the laws of physics are not cumulative in this way.
  There is only one lift-producing process. Each of the explanations itemized
  above concentrates on a different aspect of this one process.

I think this is the crux of the matter. It's sort the same story as in the recent HN post about the hazards of determining cause and effect in medical research. The laws of physics set up a situation where the solution satisfying all the constraints is that the wing produces lift. But just like you can't pull out one equation out of a linear system and say that the solution is X=13 because of this one equation, one can't say that a wing produces lift because of any one physical effect.