Alot of right handed players use a left curved stick. The thought being, that if you have your dominant, stronger hand on the top of the stick it will give you a quicker, harder shot because you'll be able to put a stronger "snap" into your shots and since the majority of people are right handed, the majority of people would use left handed sticks in that theory.
That being said, there are plenty of players who are right handed and use right curved sticks and vice versa, some think that this method improves puck control and accuracy having your stronger hand on the bottom, near the puck. It's probably just more of a comfort thing then anything else.