So someone spoofing a referrer link with curl would have free access?
Or are you also checking those referrer links somehow, to make sure they're legitimate?
I also take it from your other reply about curl (http://news.ycombinator.com/item?id=2336371) that you're using ip address, as opposed or maybe in addition to cookies to enforce the 20 articles per month limit.
First, this isn't a project I worked on directly so bear that in mind in that I cant address specific points (but will update if I learn the answers).
I will say this much; its expected that many people will find away to get around the paywall via plugins, curl, whatever. There are no illusions about that.
However this is not typical of your average user - that much I've seen. While I'm sure this will happen, and it might be easy for many, it will not be something I'd expect of most users and no something that will impact subscriptions IMHO.
Or are you also checking those referrer links somehow, to make sure they're legitimate?
I also take it from your other reply about curl (http://news.ycombinator.com/item?id=2336371) that you're using ip address, as opposed or maybe in addition to cookies to enforce the 20 articles per month limit.