If we're eventually aiming to become a site that takes in a lot of outside traffic, self-policing a la GG isn't going to be a very great idea. It works in small-scale communities with intelligent people - it doesn't work well when you have to deal with the masses.
For that reason, we probably need to codify the rules, but keep them laidback, and have moderators intervene primarily with verbals/reminders except as necessary. Enforcing a higher standard for posting quality than you see on say, the WOTC boards is probably a very good idea, but we can certainly go about that in a much less dickish/authoritarian style.
Finding some way to keep at least certain areas of the site as sandboxes free from stupidity is going to be important, too. The problem with MTG forums as forums for the purpose of talking about MTG has always been the fact that smart people don't like mixing with people dumber than them when it comes to
talking cards. To some extent there's not much we can (or should) try to do about that, but it's something to keep in mind.
One of the ways to approach the problem may be through a social networking angle. I have a few ideas on that. Nothing specific on how to go about implementation, but if the end result is that folks can put together their own private "gutters" amongst like-minded individuals, they're likely to stick around and form new sandboxes, adding considerable value.