Saw this on my weekly "deals" email:

Policy Change for upgrades using WorldPerks miles:
Northwest Airlines will change the policy on domestic fares that are eligible for upgrades by non-Elite members using WorldPerks miles. Effective October 8, 2003, T and K fares will be restricted for upgrades using WorldPerks miles, and V will become eligible. Continental Airlines fares excluded are V, Q, T, S, and L.

so it looks like they are tightening up abit on non-elites upgrading, but loosening up one fare class ("V") for them. Obviously this has no effect on NW/CO elites, but it is just an FYI for those who expect their non-elite friend/spouse/child to upgrade with their own miles.