The nice thing about wikis is that you can carry out conversations on them (with varying degrees of inconvenience, depending on the implementation) and simultaneously migrate the fruits of the conversations into more permanent pages, where they can be organized sensibly. The good stuff doesn't get lost.

Mailing lists are great for conversations but poor for organization. Who wants to search through four months of email to find vaguely remembered good stuff?

Please allow me to second the wiki idea. If we had a wiki that also had a forum module (or could be paired with a good forum system), that would be ideal.

Cheers,
Tom