We see a lot of content coming from Stack Overflow, because it's more Drupal than programming related. Questions about stuff like Rules and Views.
I can't remember ever sending questions over to Stackoverflow, maybe once in 6 months tops. If we should have a migrate path, Server Fault seems much move obvious since people from time to time ask a question about setting up Drupal on a server. We also see questions about some server config problem with a Drupal site, which isn't related to Drupal, but is a question about setting up Free BSD, linux, Windows or some other type of server.
I've seen a few of those this month, but generally it's quite rare to see questions being migrated away from the site. I don't think we see enough to make it a close reason. In time maybe, but I think it's premature. Especially since questions usually are closed by moderators anyways - not enough high rep users using the close button.