Vark.com (Aardvark) doesn't use search to try and directly answer your questions, instead they just use search to route your question to humans who might be able to answer it. So this is two levels removed from the classic search engine usage model:
1: It's not trying to answer your question directly with search, it's just trying to find a person who might be able to answer it.
2: It assumes a high initial raw failure rate (for example a high percentage of people are probably busy doing something else), so it builds-in retry routing logic. It even allows humans to help with routing.
There's a lot of hidden details in that retry logic, and a lot if it leverages social networking software, looking at user profiles, friends of friends, previous successes and failures, etc. And then many of those steps also mix in keyword search and related algorithms. On the surface might seem like a "simple" hybrid, once you see it spelled out, but they've done a lot of nice work on the details, which I suppose are proprietary.
A bit of etiquette - there's an assumption that you've already tried to find the answer on your own, perhaps with a Google, Yahoo or Bing search. You shouldn't be wasting other humans' time with questions that machines could have easily answered. Vark could qualify as a "research" engine, not just a search engine.
What Vark's network of gray-matter resources is best reserved for is the "why" or "how" or "what's the difference between..." type questions. These are the types high level or "wisdom" type questions the keyword and NLP search engines still struggle with and Vark's come up with a nice compromise.
This type of "expert locator" system has certainly been tried before, especially in the Enterprise Search market. Those older systems had the end goal of "fixing you up" with an expert via email. Vark's managing of the actual questions and answers nice and I imagine this will be the norm in enterprise offers at some point, barring any intellectual property issues. Heck, I think Vark could offer their own enterprise version.
I'd be curious to see Vark actually give me the option of searching over the previously asked set of public questions and answers. Maybe if an immediate answer isn't forthcoming from the folks Vark has asked, it could come back and at least offer to run the search as a "plan B". If it's clearly labeled and optional, and asking another human remains the primary objective, I think folks might like it.
They've also building a valuable database of questions and answers to analyze and learn from. Q&A search engines have a particular problem with Vocabulary Mismatch. The specific words people use to ask questions are different than people answering them. Some of this is linguistic in nature, and other times experts just use fancier or more precise terms than the novices asking the questions. I imagine they could mine their corpus and derive some useful relations. Even better, when vark lets a user re-ask a question, they have a chance to have multiple answers to the EXACT same question. And a multilingual vark could do this for multiple languages. Presumably this is all in their business plan, plus stuff I can't fathom. Cool!
I hope vark can continue to attract smart people!