Bill Frisell does it quite a lot too. YOu can usually get away with subtle amounts, as the neck is made to bend a bit anyway, but be very careful. You've really got to ask yoursef how much you need that sound, against how much you can potentially damage your guitar. I VERY occaisionally do it, but only as a slight vibrato for chords at the end of a song. It's really more a look thing though, to do at the end of a big song, and it's kinda like smashing your guitars - how much does look matter when you break your stuff?