First look at the official Nexus 4 bumper (Update 22/11/12)
Just found these:
Phandroid have posted a hands-on review.
The bumper does protect the glass front and back when the phone is laid down flat on either side. The brushed aluminium band is plastic not metal, even though it costs $20. No comment yet on how it affects new swiping gestures from the left and right edges of the screen.