A few years ago, I decided that I wanted to make a really good Wikipedia search engine. I downloaded the entire Wikipedia dataset, I downloaded DBPedia, I setup graph database, wrote code to query everything using SPARQL/RDF, and after much trial and error, went a completely different route: Google Ajax/JS Search API

http://chir.ag/wiki/cat+disease+brain

I did this because in the end, Google still gave very good results very fast. I made mine search-as-you-type so if I wasn't satisfied by the results, I could reedit my search text instantly.

I know because of Wikipedia's no-corporate-alliance reasons, they probably won't use Google search. If you're thinking of answering Greplin's call based on textual-analysis, my gut instinct says you will have a VERY hard time beating Google. However, if you go the DBPedia route, you might end up with something really neat. Powerset did something similar and got bought up by MS.