I've played with this a bit and have a few tips to pass along:
Favourites Guide - is also available to display the guide with just your favourite channels.
Toggle TV Aspect Ratio - will step through each of the stretch/zoom settings. When you assign this to a button and press the button, you will see a small icon in the top right corner indicating the current aspect ration. Press the button again within about 5 seconds and you will step to the next setting. This button will have no effect with a 4:3 TV.
PVR Space - This is actually a new app that displays the total GB, % available and the estimated SD and HD recording time available in hours and minutes.
This app is also available under Menu, Recorded TV, PVR Space.