Like Ctmom, I also like this kind of a response as why the Boneyard is so much fun to read and participate in. And as one who comes from a family of language professors and who writes for a paycheck, I also try to be very precise with words.
So, I feel duty bound to point out that unique has an additional meaning that diminishes the sense of one-of-a-kind, and that is that something is not typical. Thus, you can say someone's dress habits are very unique to mean that they are further from the norm then other persons, though they might not be truly one-of-a-kind.
Similarly, there is round as a mathematical principle, and round as a general descriptor. Compare a baseball and a ping pong ball. You would certainly call a baseball round, even though it isn't quite truly that due to the stitching, because it is more round than it is square. The ping pong, without the stitching, thus becomes more round.