Another note about this -- NW's web site has this news about upgrades posted:

"Currently, non-Elite WorldPerks members may not use miles to upgrade to First Class on domestic itineraries when purchasing Northwest V and K type fares or Continental V, Q and T type fares.

Due to the introduction of new classes, effective October 8, 2003, the restriction will include Northwest T and K type fares and Continental V, Q, T, S, and L type fares. Northwest V fares will become eligible for base member mileage upgrades effective October 8, 2003."

I wonder if non-elite members can upgrade Northwest L class fares - although I have yet to see a NW fare code starting with L.