Hah. I'm writing my own Stackoverflow derivative using the same technology stack - Rails, MM, and Mongodb (mostly as an excuse to learn MongoDB!). Sorta wish I'd seen this first now, though it's been a great learning experience. :)<p>(My project is at <a href="http://wowqu.com" rel="nofollow">http://wowqu.com</a> - it's quite a bit more domain-specific, but it's been a lot of fun anyhow. :)