My thoughts:
1.) Not really gonna touch this one. I've had younger and older F/As on both carriers. Makes no difference to me - I remember good service (which I've had on both airlines), as well as some service that left a little to be desired (rare on both carriers, but still...).
2.) I've met employees that have emotions that run the gamut in terms of some liking it, some not. In terms of inflight service, I'm willing to give the NW folks a learning curve for right now. There are quite a few differences between the two carriers. While in an ideal world everything would change just like hitting a light switch, the reality is that many of the NW folks have done things a certain way for years, and it takes time to adjust to change. I've never had a problem with drink presentation on NW - it's just like DL (except NW does it from a cart). Then again, I only drink soda and beer on planes (or a glass of wine if I'm on a redeye). As for the WorldClubs, they've always needed the card. Same is true for CO and AS lounges. Only time I didn't use my CRC card to enter a WC was when I used my Platinum card on the international itinerary. FWIW, Delta will be starting ID checks at the CRCs this week - one remnant of the NW side coming over. And as MikeMpls said, I've never seen any airline that will valet-check a bag on a mainline flight (though my understanding is US will do it for a First Class passenger). Still, I've never seen it on DL or NW. Speaking of valet though, I'd love to see DL go the way of NW for RJ unloading at hubs - NW has elevators in the jetway at DTW (and maybe MSP?) where the rampers put the bags into the elevator, load it up and it's sitting there on a shelf at the top of the jetway. Much nicer system than waiting by the door of the plane.
3.) Most NW planes don't have IFE simply because they didn't use it domestically. Only the 757-300s, 757-200 TransAtlantics and A330s have it domestically. They'll probably add it in to the Airbuses and 757s over time. All the NW fleet will get the DL leather seats over time - I know an A330-200 already has them. Still, I don't have an issue with the NW seats - I've been in them plenty of times and they're pretty comfortable. As for painting, NW planes will be all repainted by end of 2010.
4.) NW/DL hasn't made a decision yet on what soft drink. I tend to think they won't get away from Coke - both Coke and Delta are Atlanta institutions. That being said, I wouldn't object to DL going to AA style service, where it's both Pepsi and Coke. Though EOD, I want my Coke!