So far I like it. It's easy to configure, can be set for automatic scans and updates and I like the way it warns you about events as it is monitoring. I won't give up Spybot S&D or Adaware and consider MS's Antispyware another tool in my arsenal to protect my PC. It's too bad I never heard of this program before MS took it over, because I think I would've bought it then. I am curious to see which direction MS goes with it...stand alone app that you have to buy or a free resouce for XP, since you had to validate your copy of XP before you could download the Beta.
MS Antispyware Beta http://www.microsoft.com/athome/security/spyware/software/default.mspx
Spybot S&D http://www.safer-networking.org/en/index.html
Lavasoft Adaware http://www.lavasoft.de/