Steam Big Picture mode beta is included aswell.
There's a workaround so that everyone can use Steam right now But only Steam itself and the indie games, not the Source engine games.
Everything is working perfect for me with fglrx and Ubuntu+Unity. Even Steam Big Picture mode and even the Steam Community Overlay toggled with Shift+Tab ingame Awesome.
I'm running radeon (r600) driver (HD4850) and so far its working. BigPicture intro animation is rather slow but rest is working. Game overlay is working with World of Goo which is the only game I successfully started.
There is an issue with missing tray icon in KDE 4.9.3, so after closing all windows, steam is running in background but another execution of `./steam.sh steam://open/friends` will open friend window again.
Seams this trick might only work with 32bit installations of ubuntu. Steam installs and launches but interaction with the mouse is shotty.