We are seeing the legal issues surrounding 3D printing begin to emerge with part of the complexity being that different laws are a applicable in different territories. Papers released have looked at the U.K. and U.S. system but they do not necessarily hold true to Europe, Africa, Asia or Australia. For Australian designers there is a great resource called The Australian Design Unit which links to a toolkit for contracts, IP, marketing, financing and more. Part of the information network is an article by Design Victoria that is a specific guide to Intellectual Property for Australia’s Industrial Designers.
In Australia there is a category of 'Design Registration' that protects how a product looks, but not how it works. This is a relatively cheap protection in Australia though it is unclear how this protection transfers beyond Australia.
Copyright protects 3D designs that are artistic. To avoid overlap with registered designs, most 3D designs that are mass-produced have very limited copyright rights. This means that if you have created a 3D design for industrial purposes you will usually need to register it as a design in order to receive protection. 3D designs that have been registered have minimal copyright protection, even if they are an artistic one-off.