I came across one of Claudio Parravicini's videos on YouTube in which he plays some pieces from his Classical Masterpieces for Banjo instruction book. Up until the 20 second mark he is playing the banjo with both hands on the fretboard. It looks like quite the exotic technique.
It's called tapping. It's a guitar technique used by Steve Vai, Eddie Van Halen and poorly by many more. It seems more gimmicky to me. I don't think it's going to set the banjo world on fire any time soon.
It's a useful/musical technique when "properly" applied. I've seen electric bassists tap while playing counterpoint and contrary motion with themselves. Those weren't evident in this youtube example but it can be more than simply a performance/ "wow 'em" gimmick, musically. Some banjoist will likely take this to another level eventually.
The first time I ever saw a musician playing on the neck was Maneli Jamal. He is an extremely talented guitar player, and that influenced me to try that method both on my banjo and guitar. It sounds peaceful to me, and I hope that Bela Fleck plays on his banjo neck at Wintergrass.
That's pretty much what my instructor said. He said tapping isn't a very practical way to play the banjo since you're pretty much losing the sound boost gained by playing over the drum head and resonator, and you won't find anyone tapping who's in a bluegrass band because of those reasons. Solo classical music maybe but that's about it.