During the last three years of my first career (2006-2009), I was commuting between JNU and SEA. The JNU-SEA segment would normally occur on the late Sunday night flight, which typically had low loads. This was back in the days when the Miles and Money award ticket had real meaning, and were my first choice to buy for these trips.

When checking in, I would ask the agent if there were any upgrades available. When there were, I would usually be upgraded. Most of the time it worked, sometimes not. I would say my success rate was ~75%.