Why a 'pay for no ads' idea is a subscription to disaster: "Once a site introduces a pay-for-no-ads option, it splits its audience. A site used to be able to tell potential advertisers that their ads would be seen by some 30,000 loyal visitors. [...] [W]hat are the measurable characteristics of the two halves this scheme creates? A site's loyal readers are the ones most likely to subscribe to the ad-free version. The casual visitors are the ones least likely to subscribe. Meanwhile, advertisers will choose a site because they are interested in targeting people who are most interested in the content. And those are precisely the people who this site can no longer deliver to the advertisers."

Here's a point Evan already made in the past. I'm currently under the impression that some publishers actually gave up on advertising, and are only adding more of them to lower the quality of service of the free version. The reasoning would be that somehow this will force people into the paying service. I hold the opposite opinion that this will make users flee altogether. As I've written last year, we don't really care about your business model, so concentrate on the value proposition instead. (Update, see also The Free Lunch is Over: Online Content Subscriptions on the Rise).