This is actually a couple days old but was just brought to my attention. Valve has implemented initial support for Optimus!

http://steamproxy.com/app/221410/discussions/6/846939854395110175/

Notes:

• Make sure to upgrade to the latest build of Primus or you will experience crashes. The overlay also works.
  
• The instructions mention modifying '/etc/environment'. This is not required. To use Optirun or Primus on a game, simply modify the launch options to:
  primusrun %command%
  or
  optirun %command%

Not necessarily Optimus related but The Humble Indie Bundle 7[www.humblebundle.com] is now out. The Humble Indie Bundle 7 has DRM-free games for Linux and also includes Steam keys for all games and links to download the games from the Ubuntu Software Center.

It should be noted that not all of the games on Steam currently have a Linux version and the Ubuntu Software Center does not contain all of the games.

Experimental Nvidia drivers, recommended by Valve, are now supported by the Ubuntu version of Bumblebee. The awesome people at Web Upd8 have created instructions on how to properly install and configure the drivers here[www.webupd8.org].

Note: Latest experimental drivers appear to break primusrun and Team Fortress 2 for some people.

I have posted an experimental script for launching Source games. It includes automatic detection of 'primusrun' as well as automatic detection of the game you are launching. Check it out here.