Actually NW flights for 1/31/10 are not bookable either. I booked an award ticket yesterday using nwa.com and NW flights. An hour later it was all gone. Expertflyer can't even pull up any NW flights for 1/31/10 - but can pull up DL flights with the same flight numbers.
For now my reservation still says NW coded flights. Doesn't matter to me as long as I can get on the plane and get home.
Note: I was using my old WP number in the reservation in the hopes that EUA for award tickets still happened on NW-coded flights for WorldPerks members. I still have a slight chance
-RM