I've only missed out on upgrades TWICE on NW metal in the last year (ATL-MEM and MEM-LAX). However, I have seen MULTIPLE occasions where the agent has come aboard and paged elite pax out of coach to take the seats up front before we pushed back.

Everyone seems to enjoy NW bashing, but WorldPerks is truly a quality and classy operation. Don't worry about your upgrades if you pick NW - they are almost ALWAYS available in advance.