One important note to make here:
On that last image Gary posted, you will notice the parallel flat spots on the inner metal piece of the tensioner. Now if you look lower and to the right, you will see the threaded hole that the idler pulley bolts to. If you can imagine a centerline through the central bolt hole that also runs parallel to the flat spots, this imaginary line should "point" at the threaded hole for the idler pulley (+/- 10 degrees or so). Maybe Gary can "doctor" his image to illustrate this. For refgerence, as Gary stated, his old tensioner was about shot, not pointing at the center bolt hole for the idler anymore. I believe the actual reason for this is degradation of the rubber and the inner and outer parts slip. I don't think it's accurate to describe this damage as "taking a set". But in either case, this method of inspection should always be done to a tensioner when removed from the engine.

Gilly