What a wonderful mouse. As you can tell by the string of 5's, I really do like this mouse. First off, it was affordable, even when I bought it back 3 years ago. By now, the price must be at rock bottom.There are two choices of color for this mouse, which is a nice touch. But on to the more important things.
The mouse shape fits great in my hand, and the optical laser tracks very smoothly and quickly. The buttons are EXCELLENT. Probably my favorite part of the mouse. The standard left and right click are great. On the top near the scroll button, there are two extra scroll buttons, but more importantly, a near little button which will bring up all your currently running programs. And the absolute best thing about this mouse: two easily accessible buttons on the side which will go forward and backwards in an internet browser. There is no way I can describe the convience of being able to go back a page by hitting a button on the mouse. I cannot live without a button like this one any more.
So with such a low price, great ergonomics, and fantastic buttons, there's no reason to get rid of that old ball mouse and move up to an MX-510.