At least for questions on SFSE you can vote to close (with sufficient rep) if the question is more appropriate for another stackexchange.
Lacking the rep, you can flag a question to get a moderators attention to have them bring it over to this site. Perhaps we should all start flagging questions on StackOverflow so they get migrated over to SFSE?
Update
Started a related discussion on SO Meta, might be good to get some "we agree" comments over there as well.
Update 2
After consulting the SO meta overlords it became fairly clear that (1) migrating old content really only make sense for really good questions, (2) you can only do it once, and (3) it totally spams the front page. All in all, I think we could probably just let that one lie.
However, with regards to new questions we should all get together and start letting any new posters on Stack Overflow know about the new SFSE. As far as I can tell the majority for posters are (1) first time posters, (2) were unaware of SFSE, and (3) preferred to re-ask their questions on SFSE. This makes sense as the question volume and attention posters get (and votes answers get) is much higher on SFSE.
CALL TO ACTION
If the review queue is clear and there aren't any good questions to action, head over to the Salesforce Stackoverflow Tag and leave the following comment.
Hi @, there is a new stackexchange site specific to Salesforce
at salesforce.stackexchange.com. Come join the community over there!
:)