I sometimes fly as a non-rev on Continental. On a number of flights this summer I was trying to get on a fully booked (or overbooked) ERJ. I got on every time, and I wasn't the only one. Some of them were booked at 54 when the capacity was 50. I was completely mystified, as on the larger aircraft I have sometimes been unable to board even when there were lots of seats available the day before.

It doesn't surprise me so much out of a hub like Houston or Newark, but it DOES surprise me in PIT! That's another key: are you flying on a major carrier at its hub? Because there's a much higher noshow due to misconnects in that situation.