In an interview with Matt Haughey the $5 membership fee and advertising are discussed:

The $5 signup fee isn't subscription revenue [since it's a one-time thing]. It's mostly just putting a huge hurdle in front of having to deal with new users. 'Cause it's such a pain. The last ten years have shown that any time there's press, like the New York Times writes something about us, 300 people sign up and then wreak havoc for a while, and then go away. [Without barriers to entry] it would just be a nightmare.

Most of the revenue appears to come from ask metafilter since it is well placed for those seeking answers and services:

It's been really successful. I'm really lucky with the way Ask Metafilter works. Every question's about a topic that's easy to match ads to. The other weird thing is, ads aren't even shown to members. Members asking about what kind of digital cameras they should get want honest answers. But non-members searching for digital cameras online get [to Ask Metafilter] in that search.

Metafilter is one of the more interesting older websites on the internet. It has been around for a while and survived the early runs on trolling that younger folks and older folks that should know better do. It is interesting that it is successful in the manner it is.

Via Penelope Trunk, a study on the reasoning of entrepreneurs [pdf warning]. The study's authors differentiate between Causal Reasoning and Effectual Reasoning where the former is the domain of the business manager and the latter the entrepreneur.

Causal Reasoning is described as being based on the logic; "To the extent that we can predict the future, we can control it." This is the risk management of market research, focus groups, etc.

Effectual Reasoning is based on; "To the extent that we can control the future, we do not need to predict it." This is the risk management of find customers and see where they take your product.

While causal reasoning is secure in that there will be capital around to do the expensive market research, effectual reasoning is more adaptive to an entrepreneurs reality of having no capital, no customers and consequently operating in an area of complete unpredictability. from the study:

Consciously, or unconsciously, they [entrepreneurs] act as if they believe that the future is not out there to be discovered, but that it gets created through the very strategies of the players. ... several of the expert entrepreneurs I studied explicitly stated that being in a market that could be predicted was not such a good idea, since there would always be someone smarter and with deeper pockets who would predict it better than they could.

Another pattern that the researchers discovered with effectual reasoning, and using U-Haul as a study, was that effectual reasoning limited the cost of failure;

Effectual reasoning may not necessarily increase the probability of success of new enterprises, but it reduces the costs of failure by enabling failure to occur earlier and at lower levels of investment.

An interesting study that speaks of how to manage a business under the initial limits of not knowing your market and within the boundaries of capital and income scarcity. However, the study seems to suggest that the mindset of the entrepreneur does not change with increasing capital, income and customers.