I recently returned from a TUS-STL trip on AA with a connection through DFW. I didn't have a chance to check in online like I normally do, so I ended up checking in at an airport kiosk in Tuscon. When I got to the seat confirmation page, I was offered a $90 first class upgrade for the TUS-DFW flight. I don't get to fly first class very often since I pay for my own business travel (rather than having a big company foot the bill), so I jumped at the chance for such a cheap first class seat. My original fare was only about $200, so I got a first class seat for about $300 total.

I don't fly American that often, so I was left wondering... how often does this happen? I've always been somewhat jealous of those who get upgraded because they're frequent flyers and/or have corporate accounts, so this was quite a treat for me, even if I had to pay a little bit extra. What are the chances of this happening again if I continue to fly American?