Wow, really interesting. I remember being surprised that when I was snowboarding the camelbak I was wearing didn't throw me off, but it seems like the same "center of mass" idea as running... keep it close to where your body is used to holding extra weight and it doesn't make as big of a difference.

The worst part about wearing the camelbak (or other backpack) is that it makes my heart monitor chafe against my sports bra, easily solved with bodyglide. I do enjoy racing without it, though.