I was reading this interesting Kokorin's article, and I started thinking, well, how could a QA site make money, if you are not using advertisement?
Would your gather users information like interests and sell it to a marketing company?
Would you sell this QA to somebody else, then what? The bottom line is, if you're buying a QA website, how could you make money with it?
If you think StackOverflow doesn't make a lot of money off ads, you're wrong.
You don't need insider info to figure that out. Look at the number of daily hits they have (which they publish on their blog) and multiply by their CPM (which their ad salesmen are happy to quote you), subtract a heavy charge for bandwidth, subtract some salaries for the employees (who are publically listed so you know how many), and you'll see they're making good money.
One answer they've done is create an associated job board.
You can make money with QA sites and advertising, you just need a lot of traffic, which is very hard to do.
One way is to build a paid service around the community. StackOverflow.com for instance has built a career site. In my case (I run a language Q&A site ), I plan to launch a marketplace for translators, proofreaders and other language professionals if my site ever gets traction. I doubt I'll ever get enough traffic to justify advertising as a main source of revenue.
Another way would be to organize conferences.
In the case of Answers.OnStartups.com, my guess is that the visibility and karma that it gives to Jason and Dharmesh is very valuable by itself. For instance, Dharmesh's company sells inbound marketing software for web startups. Furthermore, if either of them ever wanted to raise venture capital, it surely couldn't hurt if the VCs were active on their own Q&A site.
I think Jason is right: if you go with advertising, you need a huge market to be profitable. But if you step back and think about it, we're talking about expertise here more than a given codebase.
On the Stackoverflow blog, Joel and Jeff claimed that they didn't have much success with Google Adsense. Even though they get 6M page views per day.
There's also this article stating that the "educated" click on ads less. Whatever that means.
Finally some audiences, like programmers, tend to use ad blockers more than others. So, I guess the audience is important.
Other obvious answers are: