"All you would need to do is follow Valve's instructions and you're ready to go."
This is incredibly misleading. If you do not have a computer with UEFI, you have specifically seek out a non-uefi version on google because it doesn't state anywhere on the SteamOS site that it even exists. Once you have the .iso, you burn the image to a dvd, slap it into the computer and you MAY get it to install, but most likely you'll have an issue like I did where it flat out refused to install part of the OS. In effect, SteamOS was dead in the water for me. I've heard of others getting it to work by messing around with the terminal, but frankly I'm not a Linux Guru, and everyone I've talk to about my particular issue said you would need to be one in order to wade through the crap to get it working. And Valve doesn't really GIVE you instructions past "unzip the contents to the USB flash drive and reboot".
This isn't to say I think SteamOS is a bad idea, it's just in beta (maybe alpha would be more appropriate, but what do I know).
I have tried using Ubuntu instead, but there's a problem there as well. Games that I've had no problem running before (team fortress 2) run SIGNIFICANTLY worse. I was averaging 15fps after installing steamOS. The system I installed it on wasn't particularly powerful, but on all low settings it should have done twice that easily.