I personally think that conversation-based efforts are best handled in (plain-text) email. Wiki efforts are good for a large number of people who are in disperate parts of the knowledge space working independently; that is: I think that WikiPedia is the only significant useful application of the Wiki technology. The problems that I have with it for either a) large numbers of people working on a small number of items or b) as a replacement for a mailing list boil down to: there's no good effective way to track the 'discussion' ... RSS has provided an interesting way to map time-series events (such as posting to a blog) to what amounts to email, but I think a mailing list with a good archive and a decent search engine is better.
/jordan