There was a baby born in China, Shanghai about a three or four ago who had an almost perfectly formed third arm - although the nerves were messed up and it was only partially functional (or so they think, the doctors weren't too sure if the arm would gain additional functionality as the infant grew). The parents had it removed, because of potential social stigma and a concern that as the arm developed muscle mass, it might impinge on the functionality of the other arms or might cause circulatory problems.
Ah yes, here is the story:
http://news.bbc.co.uk/2/hi/health/5153292.stm
As for whether or not I'd like a third arm: HELL YES. If it was fully functional and placed just below my right arm, think of the things you could accomplish. You'd be much.... handier.... in a fight, you'd be able to type AND answer the phone at the same time, hold two shopping bags AND drink a can of soft drink and hold a book open while you type from it, or hold a canvas in two arms and paint with the third.
It would be awesome.
