I've only flown DL once since the partnership began, and encountered the following:
1st Class elite upgrade? Absolutely not!
Premium advance seating assignments? No. (DL phone agent claimed she had no way to verify NW elite status)
Medallion / 1st Class check-in lines? Yes. (Showed NW Gold elite card)
Pre-Boarding? Yes. (Showed NW Gold elite card)
Crown Room Club access? Yes. (Showed WorldClub card and DL boarding pass)