Good article - thanks. It's probably worth mentioning that there are closed source alternatives out there. The open sources ones are great, but not for everyone.
The ProjectForum wiki that I'm involved with for example, is so easy to setup that anyone can do it - forget setting up databases, or even knowing what language the thing is written in. The better open source ones definitely appeal to techies, but some others may be more appropriate for a general audience - really easy to install (or use a hosted service), and feature sets that target regular users.
We gets lots of people who look at the open source ones and then pick ProjectForum; at the same time we'll sometimes recommend one of the open source ones to people who have looked at our stuff first. It's all about finding the right match for peoples' needs.