PlayStation 4's interface discussed in detail by Sony's Yoshida.
Yoshida reflects on the gamescom demo, (quotes from the PS US Blog):
“What I showed was only a small portion of the UI,” he explained. “Obviously the system software is still in development. We really wanted to show off the social aspect of the UI. The minute you boot up, you’ll see all the information about games you own, what your friends are doing, whether there’s any new DLC coming out, or if your friends have shared a video or screenshot. And you can also spectate anyone playing PS4.
“The demonstration was to show that my friend Eric was playing Killzone. I was able to spectate, but also join the game. All PS4 games allow you to take screenshots, so I pressed the share button to automatically take one. And PS4 also records the last 15 minutes of gameplay, so I had the choice of either uploading the screenshot or the video. So I tweeted out the screenshot to my actual Twitter account. And if I chose to, I could have posted the video to my Facebook. It’s very easy to do.”