i like the skull roots design, but the guitar guy is in a pretty boring pose. if you must put a musician, make him rocking out! put some passion or emotion into it, something that taps the mental capacities.
I think this is a very good design, and I think the relaxed thoughtful pose works better than a normal 'rock out' pose as it is more subtle. I think the white on blue looks best, and you have got some great detail in your linework
ps pls critique if you get a chance http://www.threadless.com/critique/12244/One_Eyed_monster