PS4 user interface and features: Everything we know so far

PSU writes:

With only three days left until launch, we've gone hands-on with PS4 at a review event in New York City. After an extended live demonstration of PS4's various applications, I left the room with pages of notes, many questions answered, and more than a few still burning. Regardless, I've got buckets of information to share about the PS4 experience, from speed to stability and everything in between.