Rocketboom interviews Garrison Keillor (a lover of encyclopedias of yore) who pronounces it "wi-KUH-pee-dee-uh". He loves Wikipedia, despite its flaws. Fast forward, if you must, to 3:15 in the interview.

Greg

I have long had great affection for Garrison Keillor and it has not been based on his being right or wrong on any one topic but for his passion for the written and spoken word. Remember that the criticisms of WP are often non-obvious to casual observers.