If you believe all those Mac commercials, then Windows has been "plagued" with security problems. Many of these problems arise from users inadvertantly installing spyware or other malware that slow things down or make your system unstable. To protect users from themselves, Microsoft has incorporated the User Account Control (UAC) into Windows Vista, which asks you to verify practially every little thing you do on your computer.
This may make Windows more stable for 99% of the users who don't know how to really use their computers, but what about the rest of us who know how to maintain our system? Windows keeps asking me if I want to wipe my butt when I take a crap. How do I turn the UAC off?