MS Antispyware review - About.com

Superb detection
Microsoft AntiSpyware (beta1) achieved an overall score of 91% effectiveness in removing the active components of the adware/spyware used in the tests, tackling:
96% of processes running in memory
67% of start/search page modifications
100% of BHO/Toolbars
95% of startup vectors
100% of other (buttons/menu items, etc)

For comparison purposes, the free versions of Ad-Aware and Spybot achieved only 65% and 55% detection respectively in the same tests.

Overall impression
It’s important to remember that these tests involved beta product. It can be expected that many, if not most or all, of the reported bugs will be fixed prior to its being released as commercial product. The unsurpassed detection rates provided by Microsoft AntiSpyware are coupled with an interface that is exceptionally easy to use and understand. This is a product that will benefit both novice and expert, and provide a significant improvement over existing anti-spyware solutions.

http://antivirus.about.com/od/antivirussoftwarereviews/a/msantispy.htm