I've had one for a couple years now... It's been a machine that I've had to tinker with in order for it to work in an acceptable manner. My biggest complaints about it are the belt wobble--solved by squaring up the drive wheels and installing a better tension spring or gas piston--and the fact that it's about as smooth as a forklift driving down a washboard road. The pulley system produced quite a bit of vibration and only gets worse as you ramp the speed up. The cheap quality bearings they use don't help at all either; I've had to replace almost every single one on the machine and I'd consider that unacceptable considering that I only use it a couple times a week at best.
Overall it's a decent machine and I've turned out a bunch of really nice knives on it, but there is MUCH better out there for comparable money. For a few bucks more, I'd seriously look at Esteem grinders. They run MUCH smoother and quieter--direct drive is the way to go in my opinion and I'm currently saving up my pennies to do a direct drive conversion on my KMG.