This is an interesting topic. I have often wondered about small shop builders buying a CNC machine and cutting out Fenders or a popular choice is the Ibanez Jem. It seems like eBay is littered with Jem "replacement bodies" and necks. Most of the necks even go so far as to inlay the Steve Vai vine inlay on the fretboard. Do you think these people could get in trouble for reproducing these?
As far as the major companies go, most courts have upheld that companies, like Fender, can't patent or copyright their specific body design because it is too vague. Look at the Peavey case. I guess theoretically Fender could probably patent or copyright their exact dimensions, but as soon as a copying company slightly altered those dimensions, they would not be infringing on Fenders' property. Plus, think about it; most electric guitars are based off of two main designs in one way or another: Fender Strat and Gibson Les Paul. The solid body electric guitar industry is a copy of these two original designs for the most part.