This was a kick ass idea. Lots of people make dress up games but usually it's crapy cartoon porn, video game characters, or cars. But a Guitar... this is actually something worth playing.
Honestly though, my only real complaint was the lack of "options" if you will. You put a great amount of time in to this and I really enjoyed how you where able to shape the body of the guitar, but the shapes where limited. They seemed all way too "Standard"... what if I want to build a heavy metal guitar? Where are all the sharp points at?
A few "fantasy" additions would be nice too. I can see how you where going more for realism here, but a few crazy ideas would just add more fun to the game.
The addition of stickers might not be a bad touch either. I personally hate punk, but I'm sure there are lots of punk kids that would love the ability to "ghetto" up their guitar by tossing stickers all over the place.
Fun little things would be nice too. Like my favorite... duck tap as a strap lock.
I know I just bitched a lot, but do not get me wrong. This is a great game. Just ideas that you might want to consider when this moves from "Demo" to the real version.