Here is an interesting and educational article from O'Reilly Radar blog on the subject of link shortening services and some of the pros and cons of them today. The basic idea is that one pastes a long link to be shortened into a window on the shortening service's site and uses the short form created by the service as a substitute for the original link.
Google has a shortening service: Goo.gl
3 links to the same book on Amazon.com look like this:
- The above is a link to Mark Epstein's book "Psychotherapy Without the Self". Here is a buried or masked link to the same book.
- Here is a link to the same book that has been shortened by Google's link shortening service, Goo.gl http://goo.gl/0Jcg