The one thing I really like about MS anti-spyware is it runs in the background. It is able to advise you when startup items have changed and sometimes gives you the option to block the changes. It monitors your home page for any changes and gives you the option to stop the homepage from being changed.
As far as scanning goes, I still like the idea of having a couple of anti-spy/ad- ware removers. Each program detects garbage-ware differently. So I always find that running a few of the programs helps remove the garbage ware. Both programs do a great job of detecting and removing garbage ware.
I have been using the MS anti spyware since it was first released and haven't had any issues with it at all. I do like that it monitors the system in real time and alerts me to any changes.
Generally I install Spybot, Ad-Aware and MS anti spyware on computers. All three are great programs and a must now a days.