The MX510 is a very well designed mouse and fits my hand well. It's been my weapon of choice for several years now and has done me no wrong. As soon as I plugged it into my MBP I noticed it wasn't working properly. At high speeds the mouse is fine. I use a SteelPad (treated aluminum) and it tracks smoothly. At low speeds it seems like the mouse sensivity changes or something...and becomes inconsistent. I've tried it on my desk (no mouse pad) but to no avail. This leads me to believe it's simply a software issue. The drivers are straight off the Logitech site. I'm confused @_@ Side note: When I boot camp Windows XP or Vista it runs just as it used to. Whyyyyyyy?