The rotors are considered worn out, when they get to .180 inches thick .
I have an LS, that the previous owner had the rotors machined to remove the heavy grooving, the thickness at the edges where the pads don't contact, were .140 inches thick .
I found between both rotors, 13 cracks that ran between the holes in the rotor .
With the grooves that were present on the rotors, there were areas where the rotor was no more than .040 inches thick .
I would check the thickness of the rotors to determine whether they are worn or not, factor in the groove depth as well .