List of the thin parts that they can't recreate well:
Fleurbine, Featherbluster, Marshcara, Peacrock, Featherferns, Grasstachio, Coverleaf, Florsage, Whipwhick, Bonestickler, Segmentenna, talkgazer
Like others have said, it's still early tech for the common man, and right now it's just a novelty. Eventually 3D printers will be as common as regular inkjet printers.
NASA has a bunch of rapid prototyping machines that use a variety of methods and materials, including titanium, and they're trying to sell off their EBF3 (electron-beam freeform fabrication) machine technology to the private sector. They use one on the space station to create emergency replacement parts on site. Pretty impressive stuff.
It's very exciting technology, especially
RepRap.