A "Spotlight" in Aperture
A few months ago, I got a subtle dent in the side of my car - so subtle I was having trouble capturing it in a picture. Finally, I got something that showed the disruption in the line of the car body. But I wanted to highlight it in the photo. Using a Burn adjustment in Aperture, I was able to make a "spotlight" on the dent in the photo.
The technique is simple. Apply a Burn adjustment to the entire photo. Then, using a hard-edged brush (zero softness), brush away the area of utmost interest.
I don't expect this is a technique I'll commonly use (except for those Sasquatch sightings I've got :), but a handy trick to have in the bag.