After seeing Lindsay, Matt, and Scott discuss the issue, I'm convinced that the central dilemma faced by nice guys has been missed. This constitutes a blogospheric emergency of such importance that I must use my position as Ezra's guestblogger to make the problem clear.
It's a necessary condition for being a nice guy that you apply high standards to your behavior with women. You deny yourself recourse to strategies that don't meet these standards. Minimally, you don't hit on girls impolitely or in inappropriate contexts, and you don't try to pressure girls into doing things that they might not want to do. You make sure they have an easy way to say no if they're not really interested -- strategies that don't leave the other person an out are rejected. Further, as Lindsay points out, "nice guys don't feel compelled to tell you how nice they are." Genuine nice guys will be sensitized to the immodesty of boasting about their niceness, and to the subtle ickiness of many other behaviors, which they will then refuse to employ.
This would be enough to put nice guys at a disadvantage -- the same disadvantage that nice people, generally, have in any endeavor. Nice people avoid immoral or even slightly sketchy means for achieving their ends, and this is why they often fail in cases where immoral means are particularly helpful. Good societies try to reward nice behavior and punish the users of immoral tactics, so as to rebalance the incentives. Dating situations, however, are often subtle enough that it's hard to do this effectively. And there's a further issue that makes the problem more severe.