What is the policy for questions that are already asked on Stack Overflow, Super User, or something similar? I've got a few questions over there that are unanswered (and some answered but I'm not fully satisfied with the answers) that would would love to move over here to get more attention. Is there a formal moving process? Should I just re-ask the question? Do I need to always cross-reference the old question?
During the private beta: if you see an existing question which has not been satisfactorily answered and that interests you personally, then feel free to re-ask it here.
Do cite the original: if you reworded the question to your liking, link to the original; if you copied the words literally, use quote markup and credit the original author. If there are answers on the original site, summarize them and indicate in what way you find them sub-par. (Here's an example from the recent defunct Operating Systems beta; the motivation for re-asking was that there were at the time two answers on Stack Overflow that seemed contradictory.)
Please don't re-ask questions just for the sake of re-asking. The point is to get better answers, not to re-do the work or “appropriate” the questions.
Once this site goes public, migration will be another option. However, on-topic questions will not be migrated away from other sites, even if this site exists. Furthermore questions older than 60 days cannot be migrated at all. Migration is only an option for a question that is off-topic or at best borderline (for example a question about general usage Emacs on Stack Overflow, that doesn't involve Lisp programming and isn't about working with source code), and only if it is recent enough.
If you find similar questions on this site and on another site after this site goes public, please comment on each site to list to the other question, so that people who find one of the questions in a search can easily check the other one for new or better answers. Do not post the same question on multiple sites.