I have to admit that I don't really get wikis. I expect this would change if I ever used one for a project. Among their big strengths, though, is that a wiki is easy to implement and easy to use. And anything that gets used is ipso facto of higher value than anything that doesn't.

In any event, here's a case study on using SocialText for product development:

Socialtext provides Stata with a shared environment to develop product specifications and work out problems as they arise. "If we have better specs up front, we have better quality software." Stata uses Socialtext to develop specifications, documentation, record agreements, solve problems.

Communication is particularly important with a distributed team. The wiki lets the right people contribute, even across time zones. When the team is developing product specs, "you get halfway through and realize that another person needs to participate -- by having it on the wiki it becomes much easier to rope that person into the process and get the context quicker." Getting the right specialties involved counts.