Also to follow up, I never did get flysong online checkin to work on those flights in June. On my outbound flight, I couldn't use online (or kiosk) checkin at all because I bought the ticket too close to the travel date so I had to show ID to checkin. I had purchased my ticket on the phone.

On the way back, I tried using flysong.com to check in, but it didn't seem to work right, so I just checked in at the airport (the kiosks didn't work either, but I think that was because my attempt at flysong somehow locked my reservation--never could get a straight answer from the DL agents).

You might have a different experience if you bought your ticket further in advance, or if you didn't screw around with your itin on flysong like I did, or if DL has worked out more of the kinks in the DL-NW alliance in the last month.

Also, all of my boarding passes (which were all issued by DL agents at counters) had my NW number on them, but I've never received WP credit for the Comair segments (only the DL segments actually posted). I'm waiting for 6 weeks to pass (just a week or so away from my June 20 flight), then I'm going to call WP and complain again. See my other thread on earning WP on DL: http://www.flyertalk.com/forum/Forum35/HTML/006433.html