John in NM
For all practical purposes, it is all fair game unless one can prove their own originality and is willing to defend it in court - as with a patent. Outside of court, the question becomes excessively subjective and usually any discussion degrades to egos and a bunch of chest pounding.

Worrying about people copying one's "original" designs is just another way to race to an already too early grave. A person capable of coming up with truly novel designs always has a huge advantage over the imitators, they can keep designing. Wasting their time worrying about being imitated is just taking time away from the practice of their true skill - designing.

I remember working for a guy who was supposedly the first in town to start making G&G inspired furniture out of local woods. He got very, very offended if anyone came in and wanted to know how we made the little square pegs or some other such nonsense. The whole thing was verging on paranoia, and really a very silly extreme to go to over what were in essence already little more than copies. On the other hand, the boss really did have exceptional taste and a great eye for proportion - I always thought it tragic that he wasted his time tying up his ego in these copies rather than original work he was quite capable of producing.