[dhgeyer]

If the pads are actually worn through, you'll hear a very bad sound when the brakes are applied when riding. If it's just a slight rubbing when the engine is off and you push the bike, that's absolutely normal. The pads are always in contact with the disk. Sometimes, like Sarris says, they'll screech almost like they need replacement just from some grit getting in there. It's so easy to check the pad thickness, there's no reason not to look up how to do it, and put your mind at ease. You don't have to turn any wrenches. You just have to know what to look for, and it's a visual check.

[edit] I just tried checking mine, and found that it is much easier to see the outside pad with a small flashlight and a hand held mirror. It can be done.