Last month I made an argument that the NHL salary cap did not have much of an effect on competitive balance in the NHL, but rather the increase in population of NHL caliber players is likely having a much greater impact on increasing competitive balance in the NHL, as measured by the Noll-Scully measure of competitive balance.
I recently found a rebuttal of my blog. Most of my comments that I was planning on making are actually made in the comments of the blog referenced by "doc", which is actually Don Coffin - an economist whose most interesting research (to me anyway) is in baseball economics. So read through those if you want to see why a salary cap should not theoretically affect competitive balance.
There is one slight error stated in the blog above, and that is on the lowest number that can occur with the Noll-Scully measure of competitive balance. The author of the blog states that, "... the lowest you can expect Noll-Scully to be is 1.000, and that's when every team is of exactly equal talent", which is not true. If every team is exactly equal, then every team will have a winning percentage of 0.500, and the standard deviation of all teams having a 0.500 winning percentage is zero. Thus, the Noll-Scully of a league with every team exactly equal in talent (and thus winning percentage) will also be zero, not one. Just thought I would clear up that small error.