I recently bought some "Wilson Pro Overgrip" to try out but after I put it on I realized that the grip was spiraling in the way that it should for a left handed player. After looking at the other 2 rolls they where the same with the end that you start with cut so that you have to wrap the grip spiraling the way a left handed person would want it. I know this is hard to understand but if you go to about 4:20 in this video it will help you to. http://www.youtube.com/watch?v=yn1cYRF5tJc
I noticed it too. Is it really a big difference? But I disliked that overgrip for other reasons. Mainly because it couldn't take the sweat from one match.