About 10 years ago I had the privilege of working with Anne Holland as she was starting up MarketingSherpa.com.  I don't exactly remember how I met Anne, but it had to be through some activity in the premium newsletter business since that's the industry we both worked in during the 90s.  She's one of the smartest people I've ever worked with and so I can recommend without hesitation, and without reviewing it myself, this free training video for newspaper execs.  Anne has started a new site, Subscription Site Insider, that I'm fairly sure will become a "must-use" site for anyone in the paid content space, if it isn't already.  From the page about the video:

During our research for the presentation we could not find one single example of a good newspaper paywall. Not one! Newspaper paywalls are — frankly — scary bad. They just ignore all best practices.

Why is that? My theory is that newspaper site design is really difficult – it’s a science in itself. You’re dealing with heavy text, complex navigation, and hundreds of thousands of pages… Plus, on top of making this dense content easily navigatible, you also have to deal with the demands of advertisers — get them enough clicks to keep paying while not sacrificing all your screen space.

Paywall design requires a completely different skill set. The goal is paid conversion, not free navigation. The content is focused, not comprehensive. Psychologically, the audience isn’t looking at the page because they want to be there, but because they’re forced to be there.

Other niches in the subscription site industry have been testing, researching and refining their paywalls for close to 15 years now. Audience development executives and web designers for newspapers can learn a lot from them. 

If your business depends on getting people to pay for access to your "stuff" then you really should check out Anne's place. You wont' regret it.