This article has interesting advice on building a good Wiki. Note that this is about the software, not content.
The author doesn't like CamelCamel case so I strongly disagree on that point. I consider CamelCase not only a good idea but essential. MediaWiki is particularly annoying on this point, though I've decided I can live with it.
The point about good search with relevant results is important, IMHO.
Looking back over it, maybe I only agree with about half of the article but I'll post it here anyway.