I flew NW recently between BNA and MGM, and I noticed several things on the flights that may add to the discussion of NW service above.
The A320 from BNA to MEM was quite comfortable. The cabin crew was fairly attentive, although for most of the flight they remained seated b/c of dense build-ups around the aircraft all the way to MEM.
NW's MEM hub is hell. Absolute hell. The terminal is old, drab, and depressing, still being in a beige '70s motif. It's also filthy. On top of that, the MEM ground staff were surly, inattentive, and abrasive.
The NW Airlink SF340 from MEM to MGM was equally nightmarish. The seatbacks (ostensibly for safety/evac reasons) only came to my mid-back region (I'm 5'11"), and the a/c was expectedly loud, but the lone F/A was extremely cordial and indicated she loved working for Express I (the Airlink carrier out of MEM). The return was the same, and my comments would be the same.
The 340 from MGM-MEM was still uncomfortable; the MEM hub was still hell. As for the DC-9-50 from MEM to BNA, however, j'ai été très impressionné! The interior appeared to be brand-new; the seats were extraordinarily comfortable. The cabin crew was relatively attentive but slightly cold and lacked the friendly touch that seems to be becoming the norm at DL these days. The flight crew was exceptionally attentive, though, explaining in detail the weather intricacies in MEM that caused a gate hold.
All in all, NW is respectable, but definitely suffers from customer service issues that need to be addressed. And the MEM hub is nightmarish! They seriously need to evaluate renovating that facility.