And of course, your chances of upgrading are greatly improved if you have status on the airline. This is very easy to get. (AA is doing a double EQM promotion right now, which means one transpacific flight gets you Gold status. With this, you check a box when making your reservation, and if there is availability in the next class of service, you are automatically upgraded 24 hours before the flight. Much better than gambling on the rare "LFBU" kiosk upgrade.)
Anyway, statistics are nice, but it's pretty easy to ensure you get the upgrade. I fly about 50k miles a year, and have only missed one segment in the last two years. (And that was my fault; I checked in without enough "upgrade stickers" and was removed from the upgrade list. I got back on about an hour before the flight, and missed the upgrade by one spot. Oh well :) I have also been upgraded for free on a variety of generally non-upgradeable segments this year, too. A very nice undocumented bonus of having status.
Stay tuned--and keep the suggestions coming. Always appreciated!
When I take a flight that's not on Southwest and more than an hour in length, I like to do the first-class / business class upgrades when I check in because they aren't that much more expensive (usually $50 to $100 per leg). It's one of my few guilty pleasures.
Anyways, it would be pretty cool if there was a way for me to predict which flights have a higher likelihood of having those types of flight upgrades available (which is to say flights that are statistically less likely to have a full first or business class).
I have no idea if you guys even have access to that kind of data, but whenever I book travel now I guess as to the likelihood of being able to upgrade on the day.