Timo Sirainen explained:
I haven't really understood why they're so great. I just looked at twiki anyway, it's what most people seem to be using. Looks a bit insecure.. And looks like it takes some work to get it into useful state.
having used twiki and moinmoin, I think moinmoin is a better system now. I've run twiki as part of IPCop and it's worked rather well. We have had more damage done to us by sourceforge than we have by vandals. I believe moinmoin now keeps track of revisions which means it's easier to recover from a scribbler.
I think part of the reason they are thought of as being "great" is because they make it dammed easy for anyone to contribute. They lower the threshold of effort needed to participate which makes it more accessible to more members of a community. I've submitted a feature request with the abiword people to add a plug-in which will make it even easier (i.e. no markup language knowledge necessary). This plug-in would allow one to import and export pages from the wiki and edit them in WYSIWYG mode inside of abiword.
---eric