I haven't heard anything about pings from the flight recorders being detected yet. Always wondered whether marine seismic vessels would be of any help. They tow very long arrays of geophones (lengths of kilometers typically). Of course the sensors are tuned to normal sound frequencies, but I don't think it would be too difficult to swap out a geophone for a sensor tuned to the ping frequency of the black boxes. There are marine seismic vessels all over the world (and, these days, probably quite a few which are idle).