i must correct you.
only when you attempt to play the game they are currently play are they then booted from the game.
And I must correct you...read the FAQ: http://store.steampowered.com/sharing
Can I share specific games, or do I have to share my whole library?
Libraries are shared and borrowed in their entirety.
Can a friend and I share a library and both play at the same time?
No, a shared library may only be accessed by one user at a time.
When I authorize a device to lend my library to others, do I limit my own ability to access and play my games?
As the lender, you may always access and play your games at any time. If you decide to start playing when a friend is already playing one of your games, he/she will be given a few minutes to either purchase the game or quit playing.
Those who claim the dead never return to life haven't ever been around here at quitting time.