My wife just got upgraded to first on a free Northwest WorldPerks ticket.
I'll probably expose a loophole to any NW agents that read this but I thought you might like to hear how she did it.
All WorldPerks award tickets are e-tickets. We live in Seattle which has e-ticket check-in kiosks. Checking in at the kiosk, the boarding pass that is issued contains no remarks on being a freebie ticket. She then walks up to the counter with her upgrade certificates and gets seat 2A. Coming home, she will not be as fortunate since most citiies do not have the kiosk system.