There's a lot of good EE questions over there. Once the site goes to public beta, will those get moved over here? I have no idea how that works.
FWIW I'd sincerely hope that existing EE questions on SO would be moved to here. There is no reason a visitor could not be redirected. I think I've seen that with some other questions. Click a link on the SO site to view the question and you are taken to, say, the Webmasters SE site. There is a note appended to the question saying it was migrated from the the other place.
I don't think it's appropriate to move existing questions which have already been answered (SEO etc).
However, if someone has moderator privilege on SO (10k rep - I know none of us are even close) then they could potentially move most/all future questions here.
To @RobertCartaino et al - The reason I think this is a valid concern is that many EE questions on SO are actually getting closed as "off-topic" or "too localized", while they would be valid here. For example, PHP errors encountered while trying to install/run ExpressionEngine.