I've been seeing more and more sites lately that are setting up paywalls. Paywalls are those features that require you to pay to view content. Many paywalls are marketed to as "premium memberships," and offer resources and content that is not available to users who have a "free" membership. Some of the sites have a flash page but if you want to view pretty much anything but ads you'll have to become a paid member.
Paywalls are good for some sites. They provide revenue to pay for site maintenance and staffing with no ads or fewer ads. They help the admin sort out the serious readers from the "trolls," by requiring payment information. If the sites offer copyrighted content for viewing, the payment information on file can help site administrators track down and contact any violators (of course, this is not fool-proof). Likewise, users who have given their payment information to the administrators are a little less likely to start trouble with other users. Again, there are exceptions to this, as people sometimes have PayPal accounts and even credit cards that are not even in their real names.
Paywalls, or premium memberships can foster a sense of community among the readership. Once readers make contacts and friends on your site, they are more inclined not to want to "lose" that by dropping their memberships. If you offer a small monthly fee with credit card (or PayPal) billing, many members forget they are paying the fee at all, and you're successful in building a membership, your site can become a steady source of income.
So if paywalls are so wonderful, why don't we all just install one right now?
Whoa! Wait just a minute. The most important part of making a paywalled site successful is knowing whether or not people are willing to pay for the content on your site. If people can easily get the information elsewhere on the web, they aren't likely to want to pay to get it from you.
Almost as important in making the decision to require premium memberships is deciding whether or not you need search engine traffic. The search engines are not going to pay to crawl your site. Your users are not going to be linking to your site when e-mailing their friends or posting to social networks because when their friends click on those links and are required to pay a fee to read the link, your users are going to start losing friends quickly.
Some people are famous enough already that they don't need search engine traffic - they generate traffic through their TV or radio shows or public speaking engagements. Major newspapers that have been around for over a century have enough clout that people will pay for their content, as they will feel the need to read that paper to keep informed of current events in their industries. That's all fine and good for them, but if you don't have that sort of notoriety to begin with, you might want to re-think shutting the search engines off from most of your content.