Working on a pooh theme here, I know... very mature. But Winnie-the-Pooh (Disney gets rid of the hyphens) is a series of books specifically targeted (in a way that, for example, mustard is not) to children. In other words, the most potty-humour-obsessed people out there. It would appear that the Pooh part of the name either comes from a swan named "Pooh" spotted in a zoo by A.A. Milne's son Christopher Robin or (as described in the first book) due to the fact that his arms were so stiff that when a fly landed on his nose, he had to blow it off. "Pooh", I suppose, is an attempt at onomatopoeia then.
Regardless... 'pooh' also means 'human excrement'. And this it is a less-than-flattering name for a brown-coloured stuffed animal. I have no idea when 'pooh' entered the vernacular, but I acknowledge that certainly in 1926, when the series started, 'pooh' might not have meant, well, pooh. However, in 2009 it certainly does, and yet Disney continues to (very successfully) flog their scatologically-named toy animals. Strange how they've never tried to phase out the 'pooh' bit: in fact, Winnie-the-Pooh is sometimes known as 'Pooh Bear', which rather accentuates it.
"Winnie", incidentally, through a roundabout fashion comes from the city of Winnipeg. People from Winnipeg think this is a big deal. It rather isn't.