With Steam on Linux getting more mainstream, there is still a complicated issue.
Whichever DE (Cinnamon is my main desktop environment), the main Steam on Linux programma works fine. But not all games play along just as well.
TeamFortress2 starts, but gives black screen (with correct sounds) with AMD Catalyst drivers (12.11 via xorg-edgers, fglrx 9.010.12) on Cinnamon (composited) desktop! Same for Trine2. The "normal" Trine2 version works just fine, btw.
Playing Cogs in windowed mode is no problem. And when I choose to play Trine2 windowed, it works like it should.
So, on a Cinnamon Desktop (with two workspaces) I can start TF2, wait till the sound plays, use the mouse on the screen edge to flip to the next workspace, then go back and have TF2 minimized (main Steam window is still open). Via window previews I can even see "inside" TF2, correctly displaying the proper menu (and even the in-game console I started).
On GnomeClassic (fallback, no effects) or XCFE desktop this does not happen.
Looks like it has something to do with Cinnamon (Compiz?), fullscreen games (other apps too?), possibly AMD Catalyst (getting an Nvidia GTX-660 GPU next week).
SYSTEM: Linux Mint 14 [Nadia] 64-bit [Cinnamon]
KERNEL: Linux 3.7.0-7-generic (x86_64)
PROC: AMD Phenom II X4 840
MB: Asus M5A99X-EVO
GFX: MSI Geforce GTX-660 Twin Frozer (2Gb)
Graphics: nvidia 313.09 (xorg-edgers)