On Friday when the SteamOS 1.0 "Alchemist" Beta was released, Valve said to use NVIDIA graphics as one of their hardware requirements. It also stated "AMD and Intel graphics support coming soon!" As I subsequently reported though, the Catalyst and Mesa drivers are present, meaning AMD and Intel graphics hardware support.
Now having my initial SteamOS benchmarks published, I tried out AMD Radeon and Intel HD Graphics on one of my SteamOS rigs this weekend. The AMD Radeon graphics booted without any issues:
SteamOS Compositor there is nothing that's NVIDIA-specific. It's all based on xcompmgr, we just all know that NVIDIA's binary graphics driver provides first-rate Linux support. With a Raodeon HD 6950 graphics card, the system booted up into SteamOS without any issues at all. The latest Catalyst 13.11 Linux beta was in use.
So if you're comfortable with the potential for Catalyst Linux issues with the games on Steam and want to run SteamOS, you should be able to easily do so. I'm running some AMD SteamOS benchmarks right now.
In regards to using Intel HD Graphics on SteamOS, when booting up the system it becomes a black screen. However, I think I know the issue (hint: "nomodeset" is present in the boot-loader), but once I have a chance to go back and try out Intel graphics later today with the SteamOS Mesa benchmarks, I'll write some more and possibly do some Intel benchmarks.