There is a beta sign up for Steam Family Sharing. Starting mid September it seems that a few lucky folks will be able to share their libraries with up to 10 people. I am assuming that this feature was designed to address Steam account user and password sharing as a method of not having to pay for multiple copies of a game. The big limitation to this system of course, being the fact that only one user can access your library at any given time (lender has priority). So I guess it's kind of like lending out your steam account or computer minus the security risk and plus the ability to use your own saves/achievements.
It is kind of a bummer that only one user is able to use the library at a time instead of say, being able to simultaneously use an account but being limited to one user per game. It is however, probably the fairest legit game sharing system that we are going to get. Also kind of a bummer that libraries have to be shared in their entirety. It's not a feature that I personally care about but I can picture parents for example wanting some ability to limit certain games. But, that is a nitpick at best.
This feature is perfect for people like us who really don't need or ever want to purchase multiple copies of a single player game, given that we sit 3 feet from each other. It's also perfect for playing games on the HTPC without having to log off or exit out of Steam on my computer. Very cool idea and probably long overdue, truth be told. Not taking your own digital security and privacy seriously is a dangerous mistake to make in this day and age.