So here's what happened: I had a MX518 that I got for my iMac, and then I found out that it had no drivers for OSX, so I ended up taking it back, and exchanging it for MX400. MX4000 has OSX drivers, but the wheel is awful. Each time I press the scroll wheel (which feels like it needs a bodybuilder to be able to press it), the thing tilts either left or right, causing it to not only activate the middle button, but also a left/right wheel button. This is very annoying. I'm wondering if anyone here is using software such as USB Overdrive like the one found here http://www.usboverdrive.com/USBOverdrive/News.html or similar. I mainly want to run it on MX518, and was wondering if the dpi switch buttons still work with it after it's installed on the system.