When I was doing ATL-SFO on Sundays/Mondays and back on Fridays, I exhausted my PMU certificates and then upgraded with miles whenever possible, and got one upgrade on an L fare SFO-ATL on a mid-day Friday flight (the SC agent couldn't believe her eyes!).
Now I am doing ATL-DFW on Monday mornings and back on Thursday afternoons. Recently, when I purchases my tickets ~2 weeks out, both flights are V0 for all Monday morning flights and all Thursday afternoon flights, so there is no hope for a T-6 window upgrade. I know that flying at these times greatly reduces my chances. These routes used to typically be 757's, and have been reduced to 738's and MD-88's, thus reducing the upgrade possibility even more. This week, I was #3 on the list with 2 seats available at the gate on Monday, and I was #6 on the list with 5 seats available at the gate on yesterday's flight.