Hello! I'm a rather infrequent Wikipedia contributor -- because so seldom is there a gap or mistake! Congrats to all contributors and Jimmy and the other visionaries that made Wikipedia possible.
I'm a big fan of MediaWiki and Semantic MediaWiki, having implemented a corporate wiki using those systems. As an ex-programmer (was good, just very stale -- jobs have changed) I'm rather in awe of the programming skills "behind the curtain", certainly little understood and mostly unappreciated by the vast world of knowledge takers. For those looking to dive into MediaWiki and Semantic MediaWiki I highly recommend Yaron Koren's "Working with MediaWiki", http://www.workingwithmediawiki.com.