Every programmer tests, but does every tester program?  I submit that the good ones do. 

Jason Darling sent me these two great articles that dig deeper into this discussion.

http://www.testobsessed.com/2007/01/17/tester-developers-developer-testers/
http://chrismcmahonsblog.blogspot.com/2007/01/developer-testers-and-tester-developers.html