What I'd like to see is a typology of communcation systems used for collaboration on the Internet. There are things like Usenet, mailing lists, Wikis, blogs, IRC, MUDs, and so on. What we seem to lack is a way of classifying these things, so it's harder to reason about them. David Crystal's book "Language and the Internet" offers a cursory examination of one characteristic of communication systems online: the immediacy of any response you're likely to get; he finds that this property conditions the type of language participants employ.
So, what sorts of features might one use as the basis for such a classification? To some extent this needs to be determined by the purpose of the classification; if you're doing discourse analysis, you're going to want to know whether you're dealing with a threaded (Usenet, Slashdot) or unthreaded system (Wiki, IRC). From a more social perspective, I'd suggest that privileged node access control (PNAC? It's that acronym again) might be important, that is, can anyone start a new thread, as on IRC, or is it to some degree restricted (Slashdot, Kuro5hin, blogs). In the more transient mediums such as IRC and Usenet, namespace policy is much more contested than the web-based spaces where it's settled or irrelevant.