I've been running Adaware for quite some time to look after any Spyware infections that might have come along from dodgy software or websites. But it's always been of case of me having to run the program every so often and remove the bad things that have placed themselves on my PC.
Microsoft have stepped up with their own offering in the form of Microsoft Windows AntiSpyware. even in it's beta form is one damn good piece of software. I think the part that most impresses me (aside from the great User Interface) is the active protection against spyware. The application constantly alerts you to any changes that are trying to be made that may cause adverse effects. For example it even notified me that Trillian wanted to add Context Items to my right click menu.
Also handy is the facility to reset certain elements of the Internet Explorer settings such as your homepage, search site and such. So should something change those entries you can easily put them back.
Now this is something that I would really want to install on my mom's PC (and will do so!). The active protection is probably the single biggest factor that will help prevent most users from getting totally infected. Nice touch!