Where I work, there are people that specialize in "ergo" and all that encompasses. They try to get people to use the mouse with their left hand, but I'm just not sold.
The main thing is that I will always want to use a right-handed mouse for gaming type applications (things where I need to be the most precise and quick).
The second thing is that I don't have a left-handed mouse to try out. Right-handed mice just feel to weird in the left hand (all that I have access to, at least).
I can understand the concept, but I don't think I'll be switching anytime soon.