If you have a question to ask, the usual step is to throw it at Google or to one of the 'answers' sites like 'Ask Jeeves' or answers.yahoo.com, and hope you get something back. In other words they are not targetted at any particular specialist group (except that you might occasionally send it to only a specialised site). As a result the answers one gets are frequently not quite what you want.
Aardvark works differently. (the site is vark.com and you need to register to use it). It works through Google chat or MSN or some other similar chat program. Once it gets a question (which you can ask through the chat window itself to aardvark) it sends it around instantly to all its registered relevant users who are online at that time. When a person registers with aardvark it asks for your expertise and that is how it makes sure that the 'right' users get the question. As a result, answers come very fast and usually from, if not exactly experts, at least those who know something about the subject. Aardvark claims that on an average it takes less than 5 minutes to get an answer from another on-line user. If you find the answer useful, you can even establish a direct communication with the 'expert' through aardvark for follow up questions.
In my experience, a lot depends on the questions and also the geographical location. Questions pertaining to say, something in the US are answered very fast since there are presumably large numbers of US users logged in at any given time, some of whom are well-informed. More esoteric questions (or exotic questions) take more time or are not answered at all. (At the time I tried it, I asked something about Durrell and Corfu since I was visiting Corfu (see my previous posts!) and never got a reply. However, aardvark did recognise that Corfu was in Greece and tried to send it to 'Greece' experts - presumably there weren't any!)
Similarly, if you stay logged into say gmail as I do, you will occasionally get questions based on your stated expertise through your chat window. You can choose to answer or 'pass'. If you think aardvark is asking you too many questions, you can set the frequency of that to something lower. I once got a question from a guy who asked how to cook a steak without a grill, since he didn't have one, but had an oven. I gave some instructions and later he thanked me (through aardvark) for helping him with his dinner! It's kind of spooky to be thanked by someone anonymous for helping with his dinner, halfway around the world :) But you can ask more serious questions. And hope to get some useful answer...and eventually provide a few too.
The only problem seems to be that aardvark does not keep the questions pending if they have not been answered, to be sent around at a later date or time. They are never sent around again. Their site has a list of unanswered questions but it's just too long to scroll through.