An independant company did a test on ALL spyware removal packages. NOT 1 OF THEM HAD A BETTER THEN .400 AVERAGE!!! Sorry, don't have the link handy, but I got it in my sysadmin security mailing list.
They recommend the best strategy is using at least 2 programs. Personally, at work I run a combination of both Spybot S&D and Adware SE daily on all of my users machines.