I've was NW Gold for 3 years, then NW-->DL Plat since 2006, until I hit DM 2 years ago and will hit DM for next year too (if I did all my math correctly!). Hit 1MM a few years back.
Nothing special in terms of consecutive years and yes, fewer and fewer upgrades. When I turned DM I got heartburn learning how to make GUC work (I think I got it now!). Sometimes you get a very special treat like my New Years treat at MSP, when our the arriving jetway was frozen and took 20 minutes to fix (it was -10 degrees) and ran to my connecting flight that still had 10 minutes left (we were two DMs) and got the door shut right in our faces when we got to the gate. So much for the Porsche or holding out the last flight a few minutes....