That's a nice search tool. I found that the relevance is not quite as good as Google (for example "howdoi get referrer url php") but this could be used when you enter a query that contains symbols.
No way to currently contribute answers. Another commenter mentioned cheat.errtheblog.com that uses a wiki system. The downside is that when the wiki fails (like right now) the application breaks.
You may want to just submit a good answer to StackOverflow and make sure it is well written and gets lots of votes.
Thanks for playing with it. Sometimes the first answer isn't the greatest but -p2 or -p3 will get it. In this case the following command gets you closer:
An enhancement I've been considering is noticing when users ask for a second or third answer with "-p2" or "-p3". If it happens often and the user never queries again after reading the second answer you can assume it is probably correct and display it to all users as the default response.
I'll be writing a series of blog posts about the architecture of the game as well as more info about the API at http://blog.wikimaze.me/
At a high level you are mostly right. The incorrect answers are generated using http://www.freebase.com/ (now a Google product)
Lots of pages have to be thrown out, but after analyzing thousands of articles it was relatively straightforward to know when you had a good page versus a bad one.