Please feel free to use this thread as a good place to ask for articles and glossary entries that need to exist and don't!
I will. My main advice to SoullessAutomaton was having a clear statement of context/purpose right at the top of the page, preferably followed by a table of contents. Wikipedia's format is the inspiration here, and it is a good one: the format is familiar and it handles the immediate question "what is this?" that is likely to be first on a new person's mind.
But, if I'm going to be a usability tester, I may be of more use if I leave the wiki alone until you all feel it's ready for a usability tester. I'm far less likely to be biased/predisposed to unhelpful reactions if I've not been watching the development process.
This site is very likely impenetrable to the newcomer. You one-box and defect on the True Prisoner's Dilemma, but is that just because of a cached thought, or is it your Tsuyoku Naratai? So I've created the LessWrong Wiki on Wikia. I'd like this to become a respository of useful definitions and links: it can support our discussions here, and create something lasting from the ephemerality of a blog.
badger already created a Wiki, but as you can see in the updates to that article badger and others pretty quickly concluded that TiddlyWiki wouldn't be up to the job. MediaWiki, the software Wikipedia and Wikia use, is the monster of them all, and will give us good support for practically anything we want to do, including mathematical notation. I've ported across a couple of articles from the old wiki onto the new, but many more are needed. The "download" link in TiddlyWiki and a text editor may help.
EDIT: Usernames are global across all of Wikia, so you may not be able to use the same name there as here. Sorry.