Recently I've noticed quite a few low quality posts made by "unregistered" users whose user name is of the form "user3####". For example, this and this. I'm sure there are a couple others but I can't find them right now (maybe because their posts have been deleted). In my experience at Econ.SE, such unregistered users almost never made positive contributions, in the form of good quality questions and answers (with perhaps only a handful of exceptions). I wonder if we could/should require registration to post questions/answers on Econ.SE. Of course this is not going to completely weed out trolls or low quality Q&As, but at least it raises the cost of trolling/low quality posts by a little.
I am aware that there are legitimate reasons not to implement such a requirement network-wide. But I think the case for implementing it at Econ.SE is strong.