I too have seen a "step-up" in DL service recently, both onboard and off. On my ATL-JFK and JFK-ATL segments last week, the FA's were extremely friendly and made sure that everyone in the F cabins had several rounds of drinks and everything they needed. Even off, I called the medallion desk a few nights ago to deal with a schedule change for an upcoming itinerary and at the end of the call, I said thank you and she said "No sir, thank you for being a loyal traveller with us. We really appreciate your business." There's something about increased service and being appreciated that goes a long way in my book.
Now if only JFK had the same attitude. I guess it's a New York thing...