While working on one of our sites at work, I had to deal with a strange bug. The rebound rate in Google Analytics was between 0 and 8%. This could be great, but it’s unrealistic, especially since our other sites range from 30 to 60%.
Turns out we had the ga.js script included twice on the page! Firing up FireBug helped detect this case (it was once included in the html head, and once created dynamically by JS in a script).
Hope this helps someone with the same problem some day