I have been using both as companions to each other for about 9 months. Both seem to catch what the other doesn't. I put AV on my father's computer yesterday, it caught two trojans that Norton or Tauscan couldn't.
Also, the new AdAware Personal is awsome, and really gets alot of stuff. Excellent companion to Spybot S&D.
Anybody with opinions on SpywareGuard and SpywareBlaster from Javacool?