We use our wiki to house our forms (Word templates), policies, and procedures. We have videos of computer processes, links to internet resources, information on how to use our phones, fax machines, and computer software. We house old documents in the wiki for "records retention" purposes.
Although not the "wiki way" we also setup a structure to our wiki so the content is organized by job. The front page of the wiki lists all of the additions and changes we've made over the past month or so.
We discussed the wiki, and how we would us it, several times before we rolled it out, but most people didn't "get it" until we seeded the wiki with some content.
There's a learning curve in how to use the software, so we trained a few people in how to post content and attach documents, and encouraged people to get content to those people.
We set deadlines for moving existing forms, policies, and procedures into the Wiki, and we removed that content from all other locations.
Finally we don't call our wiki a wiki. Everyone would giggle when we said "wiki". We call our wiki KiM (for Knowledge Management), and we have a picture (avatar) of KiM on our wiki to give her some personality.