although most people hated it, i used to love the aa.com booking system for a couple of reason. first, it allowed you to book whatever type of itinerary on any carrier. i frequently purchased other carriers tickets via the site, because often if i called an airline directly i would usually get a higher fare. it also allowed you to book itineraries taking advantage of the 24 hour int'l stop over rule or overnight stopvers in us cities without significant fare increases. i once checked dl prices to prague, then threw in a 24 hr stopover in hannover, germany for the atp tennis championships for $4!! also, because it is basically a travel agent, it often would circumvent purchase requirement rules. frequently i made reservations for flights (mostly dl) the day of departure at the three day advance price. i'd stop at aa in the airport and then go to dl to check in. absolutely brilliant. finally, other bizarre quirks such as booking an L or Q fare on one leg with a higher fare on the other leg would also slide by. and finally, if for some reason, i couldn't travel at the last minute, i could rebook the ticket either on the original carrier or aa(since the ticket was on their stock) without paying the change fee.
now with their supposed upgrades, they took it all away. bummer!!