Wow, this thread blew up quickly since I last checked it this AM. I thought I'd submit an interesting data point. I booked two one way fares from LAX-LHR, both were purchased for $635. I then went in to manage my reservations to add my Delta FF# to each ticket. One of the tickets estimates that I'll earn 21,339 miles while the other estimates that I'll only earn 3,494 miles. Both fares appeared to be the same at the time of booking so I'm not sure what's driving the difference. Just thought I'd throw that out there to see if anyone else is having a similar experience.