The SteamOS 12/19/2013 Alchemist Beta update provides Mesa 10.0.1 for the graphics driver; contrary to Valve's initial statements, Intel HD Graphics do work on SteamOS. Intel users also have a kernel fix to re-enable KMS support and Valve/Intel is currently working through a kernel panic issue with the frame-buffer console.
This SteamOS update is a big deal for Intel users since up to now there was Mesa 9.2. With Mesa 10.0, there's many performance improvements for Intel Haswell and Ivy Bridge along with OpenGL 3.3 support compared to OpenGL 3.1 on Mesa 9.x.
Audio has also been enabled now for use from the desktop session, but the default audio device is still hardcoded to use the discrete graphics HDMI audio adapter. There's also a fix specific to the Trine 2 game that was having audio issues on SteamOS.
Other changes include 3D pass-through support for the VMware graphics driver, USB auto-mounting to fix the Steam controller firmware upgrading, NTP time support, XDG directory helpers, and text feedback when building kernel drivers during first boot.
Valve also says they are working through some "outstanding interaction problems" between the AMD Catalyst Linux driver and SteamOS. AMD is working on the issue and there's hope it will be resolved soon.
More details on this latest SteamOS update can be found via the announcement posted at SteamCommunity.com.
If you haven't already checked out the Phoronix exclusive articles, over the past week I published SteamOS vs. Ubuntu 13.10 benchmarks, SteamOS vs. Windows 8.1 performance comparsion, 7-Way NVIDIA GeForce GPU benchmarks on SteamOS, etc. Many more benchmarks and other Phoronix exclusives will be coming in January.