When racing, there are a couple of things to watch for as far as your brake pads are concerned: loss of material depth (between the front of the backing plate and the face of the pad) and irregularities on the edges or across the face of the pad.
If a pad is thinner than the backing plate, you’ve got a problem. Replace your pads immediately. (See how to replace brake pads here.)
If the pads have rough edges and/or radial or longitudinal cracks across the rotor face, you might have bigger problems. Since the pad material undergoes heat-cycles under load, significant chunks of the pad face could suddenly pull away from the backing plate and cause problems with the rotors, which could lead to major failure at speed.
This kind of pad degradation can trigger crazing where microscopic cracks and undulations show up across the rotor’s surface. To fix, skim or lightly turn the rotor face to smooth it out.
Bear in mind that skimming does not represent a full-scale machine turning of the rotor. It is only intended to take “…4-6 thousandths of an inch and does not cause the discs to go below thickness’, according to specs offered by EBC Racing Brakes.
Whatever you decide to do, either pad replacement or skimming, do it before you get back on the track. For more guidance on inspecting brake pads, check out this post from BuyBrakes.com.