For me upgrades are working great on DL. Unfortunately, I have run into a problem now on NW but I'm not surprised. I have a 006 ticket with a DL-coded, NW-operated flight (LAX-LAS) on 10/26. There are R seats available but I have not been upgraded. My former NW WP Plat Elite # is in the reservation. All of my other flights on 10/26 (DL-coded and DL-operated) have all upgraded just fine).
As I mentioned, all other DL flights are upgrading on time with no problems recently. I guess NW still has issues with upgrades on codeshare flights. No big deal as I'm not likely to take the LAX-LAS flight afterall.
Good luck.
-RM