The marketing sense of the word “evangelism” was popularised by Guy Kawasaki in his time at Apple. Guy wrote a book on the subject, Selling the Dream (Amazon link) about how he did it at Apple, which I highly recommend. Guy also blogs chronically about this sort of thing. I need to find my copy again … its in a box somewhere. (My house: “Where’s x?” “It’s IN A BOX!” One day everything will be unpacked … then we’ll probably move.)
Read this post: The Art of Evangelism. Apply all ten steps to Wikipedia and Wikimedia.
(This suggests to me that free software “gateway drugs” really work, e.g. Firefox, OpenOffice, GIMP. Users care about applications; once they’re using all-free applications, swapping the OS out from under is easy and they sudenly discover their battery life has doubled from not running an antivirus. Sysadmins are already used to swapping Windows out from under a stack, putting Linux in its place and vastly improving performance. We use Wine for this on business-critical systems at work. This suggests that Microsoft’s drive to make Windows a first-class platform for open source software will in fact shoot them in the foot. I’m sure they have a game plan that says it won’t, but I still can’t see what it might be myself.)