I just read a USA Today article on Amazon Prime where frequent buyers can pay $79 per year for unlimited free 2-day shipping. While the article is fine, it almost completely glosses over why the program works.
By signing up, customers have invested in Amazon.com.
Not in the stocks & bonds sort of way, but in a more personal way. What customer would shop ANYWHERE ELSE after putting that money down? All Amazon has to do is provide their usual service (customers who pay $79 ahead of time know what to expect from Amazon) and come next year, those customers will do it again.
I don't purchase enough from Amazon to make it worth my while, but I certainly can see how many people do. Like the article says, one healthy holiday shopping list would cover it.
The question is how to replicate that for other sorts of websites. What can you do to get the visitors to your website to 'invest' in it? I don't mean just money, though it's certainly a good example, but anything. Forums are a good (if a bit typical) way to get that sort of investment. What other ways can you get people to buy-in to your site in a way that makes other sites seem like a waste of time?