The golden spiral is a mathematical concept and is a composition tool. A lot of the time, if you compose a photo into thirds (intentionally or instintively or by accident), I think there is a good chance of finding a golden spiral in there somewhere, since the two concepts are closely related. This is explained here and here.
In crop view in Lightroom 3, press O to cycle through overlays other than the grid. Shift + O will rotate the spiral. It use it to make minor or major adjustments to cropping a photo. For me, the spiral often fits more neatly in the photo at 4:3 ratio rather than 3:2.
Beow are examples from my photos.