I'd like to know what do you think about questions that are being asked simultaneously here & on StackOverflow. I don't know what's the authors' idea, to get more visibility probably? Usually these questions are very localized and of little reuse value.
You can't mark them as duplicate because it's across the site boundaries. You could downvote them + comment, but on which site? You can vote to close or flag for moderator's attention...
Few recent examples:
To be clear: I'm not talking about genuine different sources that end up having same problem (Salesforce Developer Workbench Hosted Version OAuth Error - Remote Access Authorization Error vs. http://stackoverflow.com/questions/14509377/salesforce-api-oauth-authorization-error-1800). I find it annoying only when it's from same author and posted few minutes apart.