Two examples to share:
1) Last year, I took a bump when IAH-DTW was oversold by 2. I bid $500 at check-in. But I approached the gate agent about an hour before departure and specifically volunteered to take a bump. She then made an announcement "needing 1 [more] volunteer."
2) On a different day, I also bid $500 on DTW-IAH at check-in. I flew my first segment, went to the Sky Club, and forgot all about it. I boarded near the end of the line. Then, the gate agent came on board and asked just me if I was still interested in $500. I declined so she made an announcement and got a volunteer.
Conclusions are they DO use the check-in list IF they need to, and that asking at the gate helps your chances.