While I've had some NW experiences like those posted by rwinn above, I'd like to share one to balance the books a bit.

I was returning from Singapore to Manchester, N.H., this past July on a deeply discounted economy ticket ($1,246 round trip). The last leg of the weird routing I needed to take for that fare involved a JFK-LGA ground transfer. I asked the SIN folks (standard check-in, I am not elite with NW) if they could fix things up. They did, routing me via MSP and DTW.

I boarded the airplane happy.

About ten minutes later, just before they closed the doors, one of the gate crew found me in my seat and said "We've been able to improve your routing so you'll get home two hours earlier." With that she handed me new boarding passes.

This was done AFTER I had left the counter, AFTER they had done all I asked, AFTER they had made me happier than I expected to be, without the slightest request on my part, and requiring a voluntary effort on theirs.

It may just be Singapore, but at least that part of NW is more than OK in my book!