I vote for a dragging caliper. If the slide pins were bad, then the two pads in the one caliper would wear unevenly. Given that the two pads are worn evenly, but more than the other side of the car, the caliper is sliding OK but is remaining applied.

I can think of two possible causes. One would be a failure of the piston to retract. Check the piston dust seal for obvious damage. You will have to rebuild or replace the caliper to remedy this problem.

The other possible culprit is the flexible brake line. These become suspect once the car reaches ~10 years of age. They can swell internally, and act as a one-way valve for the brake fluid, causing the caliper to drag just a bit.

Given that brake lines are only 15 bucks or so, I'd replace it anyway when doing to repair. It's cheaper than burning up pads and rotors.

- JimY