I started this thread after booking on Orbitz and went to bed feeling troubled. I woke up this morning to find that Orbitz had sent me an airline ticket number. I looked this up on Delta.com, and it showed "reservation confirmed" with seat assignments. I have never run into this type of circumstance but assume I definitely have a confirmed ticket to travel?!

Thank you so much to all the above posters' input! I felt much better after reading about your experiences with Orbitz. Perhaps I will use them again.

Out of curiousity, does anyone know whether Orbitz functions as a consolidator, buying large chunks of airline seats for resale in the way that hotels.com does for hotel rooms? That would explain how Orbitz had available coach seats on a flight that Delta.com showed as sold-out in coach. Alternatively, perhaps Delta allows certain large travel agencies to oversell their flights by a pre-determined number of seats?