Please check that your video card is running OpenGL version 3.3 with at least 512MB of Vram. The SteamOS version requires this as a minimum hardware configuration.
To check your hardware, select Help from the Steam menu, then System Information.
We're working on updates to address issues with the various Linux OSs out there, starting with Ubuntu.
If you are still running into problems, please open a ticket with us (firstname.lastname@example.org) and include a copy/paste of the Steam system information screen.