Sometimes the problem is the weather at the destination, although some of these weather or flight equipment cancellations are suspicious. On my last shuttle trip from LAX to SFO I arrived at the airport well in time and asked to be put on an earlier flight, which they did, and then they cancelled the flight due to equipment problems so I ended up on my original flight. Better safe than sorry though.

Can't give you any tips on free upgrades although recently I was pleasantly surprised when I took a tip from my fellow frequent flyertalker gurus and got a free upgrade at SFO when the agent did not ask me for an upgrade cert. The other legs of my journey were all on Shuttle flights where I get a free upgrade so this was the first trip where I got a completely complimentary upgrade for the entire trip.