Well, I just recently began using it and writing articles about my RP nation for it, and I noticed some major problems:
->Seemingly no spam protection. Someone had spammed two pages of our Wiki with various disgusting ad/virus links (the names were disgusting; I'd never open such pages o.O).
->Image Upload disabled. It is neither possible to upload images nor to link them. Please change that.
->Wiki is not very well known and rarely used. Maybe we can include a link to it on the forum bar (where "Home", "Help", "Search" etc. is)?
->Missing templates. The official wikipedia has a lot of them, and many of them are very useful. Maybe someone with access to the server could import them?
->Wiki Admin: Is there one? It should be clearly listed on the main page who is responsible for our wiki. If there is no one yet (or, at least, no one who has time for it), I'd like to take this job.