Ever seen the 'For the love of God' clip from Steve Vai, it's almost disgusting to watch how much facial expressions he does with it. Just as example

I have some friends who move their lips too when they play but they think I'm joking :-) I really wouldn't know about myself, but I think I put on a sour face :-)

Ha well, if it doesn't affect your playing (like your tongue hanging out muting the strings or something) it's ok for me. I think it can be funny some times too.

Latz, Gulder