I think that it all depends on the details of your situation.
1. Macs. Yes, switching them to Macs will eliminate your support time, but it isn't a cheap solution.
2. Linux. It's fine for some people, but switching to Linux to reduce support time is like switching to Zima to reduce your bar tab. People who don't want to learn about tech won't like any flavor of Linux.
3. Windows. If you stick with Windows, install Firefox with Adblock Plus. Delete all IE icons. Move them to web mail. Make a disk image of each machine. Disk imaging software will save you a ton of time on the occasions where a reformat is needed.