I've seen a number of articles recently on a variety of systems that let people ask questions and have them answered by "experts."
In the old days of the internet (pre-WWW), the average Joe would be out of luck. For the non-average, you might find an email listserv through your friends and colleagues on a topic in which you have interest. Or, if you had internet access through your job or university, you might find Usenet newsgroups, which were loaded with discussion groups of all sorts. (There were also dial-up bulletin board systems on which there were Q&A discussion boards.) These systems still exist, with many mailing lists powered by YahooGroups, Google Groups and other big providers. Newsgroups still exist, as to smaller mailing list tools.
The thing that amazes me today is the proliferation of the more generic services for asking and answering questions. These services aren't geared toward any particular specialty. Anyone who wishes to sign up, can do so and can begin answering and asking questions. And while their audience isn't people with a specific expertise, they do seem to appeal to certain audiences. I'm guessing this is based on how the word-of-mouth network drew people to the service in the first place.
Below the fold, I have a quick description of Yahoo Answers, Otavo, Wondir, FAQQLY, and Lazyweb. Obviously, these are not the only systems / services where people can ask and answer questions. And topic-specific mailing lists and bulletin boards will continue their utility for a long time to come.
John Tropea of Library Clips has been writing about this too, such as in this post on FAQQLY (and several others).
Yahoo Answers has a wide swath of people asking questions all over the map. I've used it with mixed results to ask technical questions, and I've answered a number of questions in that general area. On the down side, there are an amazing number of people asking homework questions (and people answering them).
Otavo treats the Q&A process as "quests." I like the concept they have around "joining a quest," whether that is merely answering a question or following a longer project which have multiple branches. You can see recent quests (even in a web feed) as well as quests with the most activity. And you can track individual quests ("join" a quest) to see updates on a separate page -- or you can subscribe to the feed of the individual quest.
Wondir lets you ask questions and scrolls recent questions on the main page. This particular service lets you view and answer questions anonymously, rather than requiring a user account of some variety. For some reason, there are a lot of women's health-related questions. As with many services, questions be categorized, so you can filter to the variety where you might be able to answer.
FAQQLY is a Q&A service coupled with social networking. It's name comes from the idea that you set up a FAQ page for yourself (here's my lame page), where you have questions you've answered (FAQ's), questions you've asked (Helps), and items/services you'd like to share (Shares). You can also join groups, add friends and do other social-networking-like things. Unlike the "river of questions" model of many of these services which show all the questions that come through, you only see questions of your friends and groups. (You can get to other questions, but they aren't front-and-center as on many other services).
Lazyweb was setup as a semi-permanent service by Ben Hammersley to let people ask questions, primarily of the blogosphere. I vaguely recall that it had a "post a question" interface, but now it relies on Trackback pings to pose question. Answers can be posted directly to Lazyweb or by heading back to the original blog where the query is posted.