I use:

• Windows for daily activities, and to earn my daily bread---for example, this site is prepared on a Windows box;
• Open BSD, an open source operating system which offers security, for my servers, including my internet connections;
• SuSE Linux and Free BSD for occasional extra income;
• Bell Labs' Plan 9 for interest.

There are some interesting things going on in the OS world. Visit OS News to find out more.