[TrevorJ]

After time they really don't feel clumsy at all, that's what is amazing. To get a grasp on just how integrated a tool (Or better, a musical instrument) gets, try using a common device with the opposite hand and feel how clumsy it it feels in comparison. That's the natural pre-integrated state. Part of what is happening is that the brain actually devotes more neurons to the hand that is manipulating the tool. This probably makes up somewhat for the fact that the tool itself has no sensing ability.

The mind map for the hands of professional piano players have many more neurons devoted to the hands than in normal people for instance.

Classical guitar players use their fingernails to great effect when playing to generate widely variable sounds depending on how they employ them. One could argue that you fingernails function much as tools do in this case in the sense that they don't have nerve endings at the tips but instead transmit feeling through vibration down to the nail bed. The same thing is happening on a larger scale when you hold a screwdriver, the resistance and vibration is transmitted down to the hand which senses it. Over time more neurons get devoted to those sensing and manipulating areas.

More info here: http://health.howstuffworks.com/brain8.htm

And here: http://en.wikipedia.org/wiki/Sensory_homunculus