Bambi Francisco is right. Relevance always has, still does and will forever rule. Nothing new there, but what will be new some time in the future is the use of wikis as the backbone of search rather than Google and their ever-changing algorithms.
You're using the wikipedia today to solve some of your search needs? You're not alone. But what's going to change is where the wikipedia goes from a community-driven encyclopedia to something much more flexible and powerful for other types of searches. Or at least that's my hope for the Search Wikia project that's still apparently only in the design stages.
I realize the print encyclopedia is only useful for certain types of research; you have to look elsewhere for the answers to certain questions. That's not going to change on the print side. That's also the case today for the wikipedia; Google and other resources offer better solutions. The difference is that the wikipedia can evolve but the printed encyclopedia can't. As the number of wikipedia entries grows, it starts to offer the types of answers that can't be found in a print encyclopedia. Plus, I think it's a safe bet that the Search Wikia project won't just be using the wikipedia content as is. If they're smart, they'll be able to tailor the results based on the request and not just dump a bunch of article links at you.
Here's a really simple example... Let's say you want to know how old George Washington was when he died. Do a Google search and you get these results. The answer isn't there, but it's just a click or two away. Why doesn't Google open the results page with the actual answer to my question?! Why? Because that's not how Google's search tool is built and therefore how our expectations have been set. (I'm sure ask.com would get the job done, but who uses ask?!)
The Search Wikia folks should be able to use all that content in the wikipedia and just give you back what you need. Sure, they'll provide additional links in the event your answer isn't right there at the top of the page, but hopefully they'll build a system that draws effectively, with a high degree of relevance, from the wikipedia itself.
So Google is the clear leader today, by far. They've got the brand, and to be honest, because of how our expectations have been set, they generally deliver the goods. But I'm starting to appreciate just how much better the search experience could be with Search Wikia and I can't wait to try it out.