Summary: The mouse wheel for this mouse started sticking. Also, the three dpi settings buttons in the middle were too easy to hit accidentally while using the mouse, so I ended up setting all three to the same dpi. I ended up replacing this with a mouse from Logitech, and it doesn't have any of the same problems. I've used the replacement for at least a year now, and wish I had saved the money and just gone straight to that.
Summary: I'm unsure why others feel the vertical side buttons are a great design feature. I think they protrude too far from the mouse and I often find myself accidentally hitting them. For obvious reasons that causes a lot of problems in-game. Moreover, while it could be due to the fact that I've been using a Logitech G5 for the longest time, the vertical positioning of the side buttons does not feel comfortable. Overall the mouse feels cheap.
Summary: This mouse is responsive as any other gaming mouse on the market but you have to be a mouse palmer with big hands. This thing is like pushing around a brick, it's huge. The verticle side buttons are awesome but can sometimes be hit by accident when lifting the mouse to reposition it. If you have a big hand go for it, but if you have small hands go with a Logitech MX518.