Good news, curious early adopters: if you want to try out SteamOS, you no longer need to dedicate a box solely to its operation. The initial release of Valve's Linux-based OS wouldn't let you run more than one OS out-of-the-box. An update to the SteamOS beta makes dual-boot installation much easier, though Valve engineer John Vert warned that it's still mostly untested.
"Please note there has been very little testing on this, especially any kind of dual-boot setup," Vert said on the Steam Community forums (via Polygon). "So don't install it on any machine you are not prepared to lose."
If that stern warning doesn't scare you away from trying it, you can set up hard drive partitioning through the "Expert Install" option. Dual-booting was technically possible before, but it was a more complicated process and didn't work from within the installer.