Thanks for the info Darren. Sounds promising!
We've gone with MediaWiki (the one that drives Wikipedia, can also scale very well) at work and although we aren't at a deployment stage yet I can say that its working very well out the box, the main implementation issues we have are 1) branding 2) setting up permissions (our audience is entirely internal) and the various config options; and 3) intergrating our organisations login system with the wiki (single sign-on)
In the JC case 1) would surely be applicable, but this can evolve over time without affecting the functionality and its fairly trivial anyhow. Regarding 2), this takes some consideration in the initial setup, but again can be tweaked over time. I imagine that it would be desirable to do something similar to 3) such that forum login and wiki login would be the same. I haven't had a good chance to look into the technical feasibility of this, although from past experience will similar systems it's usually not too much of a drama.
So getting a basic system up and running is pretty easy, tying it into an existing environment takes a bit more work but isn't a huge issue.
Anyway its great to hear interest from the guys in charge. I'll leave you to have a play with it yourself in a sandbox environment, but if you want a hand with anything drop me an email or a PM, I'm fairly handy with a handful (no pun) of technologies.