If in doubt, change 'em out.

Most pads come with a soft metal tang on the side of the pad. If the metal tang is touching the rotor, like an oil light being on, it was time to action before now. The tang is purposefully made of a soft alloy so that it wears instead of your rotor, and still lets you know that your brakes would really like to be changed.
Take a look at yours and if the tang is rubbing, or getting close, you should probably consider new pads.