BugMeNot: bad news for ad-driven sites

Via Lockergnome, I find BugMeNot, a site that provides registration codes for tons of sites that require “free registration”. The NY Times is one of the best examples of this. One interesting thing about this is that this turns into a data point for those sites. It tells them how many people dislike free registration so much that they would hop over to another site to get a password. Sure, if they see a lot of people using a password from BugMeNot (or if they just monitor BugMeNot themselves), they can keep this from working. But will they? And how important is a couple fields of demographic information to advertisers?