We now have the answer to one of the great riddles of the ages: How long does it take F&SF to reject my most recent submission? In this case, 7 days.
I mailed the submission on July 27 and received the rejection today, for a grand total of 7 days. It was an "alas" rejection from Gordon Van Gelder, which was actually dated on July 31. This was well under their average response time of 12 days, per their Duotrope listing. Talk about speed.
There was one outright winner, who will receive a copy of David Hartwell and Kathryn Cramer's anthology Year's Best SF 14 (which includes my Interzone story "The Ships Like Clouds, Risen by Their Rain"). This winner picked 8 days. There were also four people who picked 9 days. I'll throw their names in a hat and draw the final two names to receive copies of the book.
As for all those who picked 10 days and up, I guess you were being too kind. And before people feel too sorry for me, I also received a very nice acceptance today for a different story. Once the editor says its okay to announce the details, I'll spill the complete beans.
Thanks to everyone for taking part. I'll mail the books in the coming days.