just booked SEA-MSP-IAD/DCA-JFK-SEA for next month ... I was satisfied with the seat maps, so I checked the "request C+ upgrade" box and picked normal exit row seats on the first three segments plus a random window/aisle pair on the 763 ... got the UG email maybe 5 min after purchase, went back into My Trips, and moved us to front row window/center on the narrow-bodies and exit row window/aisle on the 763
I'm really very pleased that DL and AmEx got their act together on this ... we have a Los Angeles trip coming up in the fall, and were willing to fly SEA<-->SNA/SAN since the standard coach seats in the E75 are perfectly tolerable for 2-1/2 hours