In my haste to get ready for a track day, I had to improvise and ended up using some older brake pads.  After less than 1mile test ride, my rotors looked like this.  



By the way, here is a pic of my bike after fitting the rear tail section:

That tail looks sweet
Is it off a 250 ?

If, when you run your fingernail across the disk, your fingernail hangs up; it's usually a good idea to replace the rotor. Reason being that that little groove causes excessive heat and may warp the rotor or fade brake feel, but we are a frugal bunch so I really wouldn't worry about it. It's not like you're racing. I mean, going that fast.