This guy is playing a fretless guitar using a violin bow. I thinking about this idea a couple of days ago. It's gives an pleasing sound. I was thinking of coming up with my own instrument like this but instead make it small enough to play like an violin and change the guitar tuning to a closer tuning like the violin.

Anyways, watch:
http://www.youtube.com/watch?v=dy94L1hDHvM

Wow! That's some awesome stuff.