What I have for my laptop (which I find works beautifully) is removable hard drives.
On desktop PC's, the removable SATA bays cost very little... laptops they are a
bit more expensive as they tend to only be available from the manufacturer.
My main HDD in my laptop contains my default
operating system. When I need to do any development work
etc, I have my CD drive in the removable drive bay, and I can work away as normal. When I need to run a show, I shut down the computer, flip out my DVD drive, flick in my show drive, and boot up. My BIOS is set to boot off of of the removable caddy first, then default to my hdd, so I get loaded into my show
operating system automatically. All my development files are there on the main HDD, so I can just load them from within my show
operating system, and BAM! Ready for the show, without all those pesky background applications and glitches that my main OS has. Works exceptionally well.