Starting now, you can share your Steam library with up to five other Steam users on up to ten authorized devices.
There are a few rules and exceptions to this library sharing business, so keep the following in mind if you are planning on opening up to your family or close friends. You must be online to play games that have been shared with you. There is no pick-and-choosing what you want to make available, your entire library must be shared. Due to third-party restrictions like codes or subscriptions, some shared games will not be accessible to those borrowing from a family member's library. Most importantly, both the lender and the borrower cannot play from the same library at the same time. The account holder will have unrestricted access to their own games, but the borrower will be given a few minutes before being kicked from their game if the lender decides they wish to play. Also, region-locked content will remain region-locked.
With those caveats, this still sounds like a great step forward for digital content. In a way, this might recapture the feeling of taking a beloved game over to a friend's house to let them give it a try. It isn't exactly the same, but it is better than having your account locked to one or two computers.
For instructions on how to enable sharing, refer to Valve's announcement:
"To enable Family Library Sharing, first be sure you have Steam Guard security enabled via Steam > Settings > Account in the Steam Client. Then enable the sharing feature via Settings > Family, (or in Big Picture mode, Settings > Family Library Sharing,) where you'll also authorize specific computers and users to share."
PC gaming crowd, what do you think of Family Sharing? Will you be making use of this feature?