I haven't tried Yik Yak as it seems like a black hole of drama and ignorance. However, I think it is being used in interesting ways. Students were able to use it to severely disrupt a frivolous and disruptive class requirement. It's potentially very democratizing, though perhaps it's only bringing out the worst aspects of democracy.

http://emutalk.org/2015/01/a-new-faculty-challenge-fending-o...