We all know that sharing physical games on the PS4 is dead easy. Just check out the video embedded at the bottom of this post. However according to the just published official Playstation 4 system FAQ, sharing digital games is going to be a little more complicated (although still pretty easy).
What you’ll need to do is select one particular console as your primary PS4 and this is where all you digital content will be automatically downloaded (i.e. the system in your bedroom/lounge/house). It is also the console that will link up with your PS Vita if you have one. Any user whatsoever will be able to play the games on that console too, no matter what account they are logged in to.
As for other consoles, like if you go to a friends house and play his or her Playstation 4, you can log into your PSN account there and download games and play them, but they will only be playable via your account.
The FAQ also tells us that the friends limit for the PS4 is 2,000 in total.