Sharing digital games on the PlayStation 4 is just a little bit more complex than handing over a physical copy.
Sony made a pretty big deal about the ease with which PlayStation 4 owners can share games back in the summer, taking full advantage of Microsoft's shockingly weak performance at E3, and it holds true as long as physical copies of games are the matter at hand. When it comes to digital titles, however, the process of sharing becomes a little more complicated.
According to a newly-posted FAQ, you can activate one PlayStation 4 console as your "primary" system, and anyone who uses it can play the games you've downloaded without requiring a login, as well as take advantage of "certain" PlayStation Plus benefits if you're a member. That much seems simple enough.
If you're on another system, however, you'll have to sign into your PlayStation Network account in order to download and play games, and the games will only run when that account is logged in. PlayStation Plus benefits will apply when you're logged into a non-primary console, but again, only on your account. You'll be allowed to use two systems concurrently: your primary console and one other.
You apparently won't be required to activate a primary system but doing so provides a number of benefits including digital game sharing as detailed above, plus the ability to preorder or purchase content through the PlayStation App and have it automatically downloaded to the console, and to connect to the PS4 with a PS Vita over the internet using Remote Play functionality.
The FAQ also notes that the PS4 will support up to 2000 friends on PSN and display them all when connected, vastly surpassing the 100 friend limit of the PS3.