Two items:

Flying back from Honolulu to ORD in December on a rustbucket DC-10, they had to rope off the last 11 rows because the emergency exit in the back of the plane wasn't working. Thus, they had to make sure that there was nobody sitting in rows that have, as their primary escape route, that door. They moved a whole bunch of people from the flight to the AA flight. People on the UA flight couldn't even go back to those rows to stretch out across 5 seats. The seats were totally off-limits.

Second, I have noticed that on some widebodies, especially 747s, the last few rows of coach (not the center portion but the window portions) have a little more room because of the tapered effect of the plane. Therefore, instead of 9 seats across, there are only 8. My favorite row is the third to last row on a 747 in the window seat. Lots of additional room compared to the average coach seat. But I'd still take a business class seat any day. And I promise not to steal any anymore.