You'd think that there'd be a low Q/A rate, but apparently it depends significantly by tag, with some tags having low rates (10-20%: http://minimaxir.com/img/stack-overflow-tags/acceptable_answ...) and some having high rates (60%-70%: http://minimaxir.com/img/stack-overflow-tags/acceptable_answ...)

And some pairs do better/worse than others: http://minimaxir.com/img/stack-overflow-tags/so_tag_adjacenc...