With the move to Stack Exchange 2.0, some people feel that there will be (have been?) many more first time users asking questions on MO which should instead be asked on MSE. Presumably, such a user had to make a choice between MO and MSE (they may crosspost, but I don't think this happens frequently).
Would it be OK to ask such a user why they chose MO over MSE when letting them know that their question isn't appropriate for this site?
Maybe the replies to these enquiries may suggest something we could do to minimise such behaviour.