If you haven't already, you should set aside $60 and order the PlayStation Camera (formerly referred to as the PS4 Eye) right now. That's how well voice commands work on the console, which makes it even more curious that Sony chose specifically not to highlight this feature -- comparisons to the Xbox One's Kinect control, notwithstanding. You won't get to enjoy the full suite of commands out of the box, since prompts for "Power," "Back to Game," "Take Screenshot" and "Log in" (the four basic home screen commands) are part of the Day One update.
What you will have hands-free access to is the "PlayStation" command prompt. Say that out loud and the system will ask you to select a game or application and then say, "Start." Don't be surprised to find yourself yelling at the PS4 in different volumes the first few times you initiate the "PlayStation" command. Finding your perfect voice for control takes a little experimentation and, in our experience, a soft, almost quiet tone works best. Though that all depends on the noisiness of your home environment.
PS4 before the 1.5 update
Seems like the entire voice command ability is more advanced than was thought. I understand why Sony aren't broadcasting the ability. I think. It's either because they don't want the kinnect comparisons or they view it as a sleeper function that will have a much greater impact if spread by word of mouth and not a marketing department.