Move the wiki somewhere where they don't even have to leave their normal flow of work. We moved ours to github. Just make a private & empty repo, add a wiki to it, and now you have a wiki you can edit in your favorite editor, search with grep, and save / revert with git. Back of the napkin estimate, I would say we have 4 to 5 time the activity on the wiki that we did before. We found that developers really don't want to leave what they are doing, open a browser, possibly log in somewhere to edit in some embedded editor that doesn't have emacs/vim/whatever bindings. If your team still doesn't use it, well then it might be time to polish off that CV.
I like this - I certainly lose steam when having to login to another service to do it. Certainly worth trying. Couple of follow up question: Which wiki do you use?
