I've thought about it quite a bit, but I have never heard of or seen anyone doing it with cannabis. If the California drought continues, it could provide a viable way to significantly reduce water usage which is what really peaked my interest. I'd love to see someone take the plunge and try it out.
It can certainly be a very productive way to grow other crops - there is farm not too far from where I live that has had great success growing organic lettuce and strawberries this way. Their produce is top notch, and the minimal amount of water they use makes it even more impressive.