the manual says lots of things, like editing of the recorded shows, automatic detection of the ads, chapters creation... I could not find a way to use any of those as well...
but I did not notice the picture-in-picture feature in the manual. I am talking about the manual in pdf installed with the application version 5.1.
One thought: if you watch tv and press "Back" on the remote, the tv show goes into a small window in the lower left corner and you have the main menu in the main window. But I do not think they call that PIP ... !
or maybe they mean that you can use the PIP feature OF YOUR TV (if capable) to display the Powercinema window (coming from PC or HDMI connection) and the image generated by the TV's own tuner. I can do that on my tv.