I just read WPC's article about the Lumia 920 falling off of surfaces, and responded because I have indeed experienced the slipperyness of the 920.
Unfortunately, my friend took it a step further and slid it back and forth across a table, for an "Air-Hockey" effect, which worked, but loaded up my 3 week old 920 with scratches. Not sure if I should get it fixed or try to ask for a new phone. Either way, the next one will have a screen protector on it! Life happens!