That might have been so a while ago with the international birdies and/or BE cabin. Lately, heck almost all of 2012, plain simple F seems to be held back on even the most ridiculous routes. FCM at its very best.
http://img11.imageshack.us/img11/7393/dladvupg.jpg
I was on DTW-ATL (which I never expect to get an upgrade on) last week but it was Saturday. The first class cabin was almost entirely empty on a 757 and I was #1 on the list as a GM. I was a little shocked that it took until right before boarding for myself and a bunch of other lowly medallions to get bumped. Judging by the number of people called to come get boarding passes after upgrades had been cleared I don't think anyone was pre-upgraded.