People often expect a media to engender community: "I'm blogging but not getting enough comments!", or "if I put up a Wiki, they will come." But if you look at the amount of blog dead wood — some estimate 2/3 of blogs never got out of infancy — this is clearly not the case. The degree to which the community and media prompt and depend on each other can be complex, and differ across media genres. A common form of this mistake is what I refer to as the "fat end of the scale" fallacy: people look at the "fat" part of a scaling system and think, "Wow, a Wiki could support 1000 different collaborators." Sure, but even systems that scaled to 100,000 start small; it is in the genesis, the first one to three folks collaborating, that the community is born and the ball starts rolling.
My current belief is that Wiki's are inappropriate for starting a community. The best way to get a Wiki rolling is to use it as a collaborative "white board" for a pre-existing email list or IRC channel. People scribble to it and reference it, and that prompts others to investigate and perhaps contribute. One reason for this characteristic of Wikis is social psychology. The norms surrounding stepping on someone else's toes when editing or deleting their text are powerful: they inhibit participation or prompt easily hurt feelings. Having an existing community where the participants know each other and the community's norms mitigate this deficiency.