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.