Long live the days of the empty middle seat

Most U.S. airlines are reporting that planes are the fullest they have ever been in operating history according to the U.S DOT Bureau of Transportation Statistics. This has direct implications to passengers.
LOAD FACTOR BY YEAR
2006 79.2% (percent of seats filled on aircraft)
2005 77.6%
2004 75.5%
2003 73.5%
2002 71.8%
2001 70.0%
2000 72.4%

First, on average, you're more likely than ever in history to not have an empty seat next to you. So don't you dare move that armrest in the up position just yet.

Second, and probably more significant relates to cancelled flights. A fully booked flight where all seats are taken, then subsequently cancelled by the airline, can become a battle (or war) trying to accommodate all those unhappy folks on other flights. Less of a problem when planes were less full. Ahh, remember those days.
Third, if you are flying standby it also becomes more difficult because - you guessed it - there are fewer seats likely to be "open" for you to slip into. Miss your flight, and you may have a long wait at the airport. "Grande Latte please..."
Of course loads vary by time, market and revenue management techniques by the airline.

But, overall, those planes are running pretty darn full these days. Northwest, JetBlue and United have 2006 loads of 84%, 81.6% and 81.7% respectively. Southwest and AirTran have the lowest loads, 73.1% and 72.8% during the same year - meaning on average those planes are only about 3/4 full.