I have booked many flights on-line and should make AAdavantage Platinum for the first time late this year. I've found that once I book travel on aa.com, I can get a restricted premier seat assigned to me by immediately calling the Gold/Platinum desk and asking for a seat re-assignment.

Although the on-line booking bonus can be attractive (e.g., 2000 miles per booking with NW now), the airline's site isn't always the cheapest site on-line. Today I found an itinerary for PHL-LGW-PHL on American which was $442 round-trip on aa.com but only $417 on expedia.com. The 1000-mile ($20) bonus from aa.com wasn't worth it for an identical itinerary. When I called tech support at American and even provided them the fare basis code for the booking, they couldn't match the $417 fare! By the way both fares included all PFCs and taxes.

This itinerary is PHL-MIA-LGW and returning LGW-DFW-PHL. Even under the "Choose by Schedule" option, aa.com would not offer this itinerary, probably because most people would rather fly more directly to London. Tech support at aa.com showed me how to force the itinerary to be shown by breaking it down with the "multi-city" option on-line. Interestingly, when I tried to reserve (not book) it this way, the page crashed, even though my computer didn't.

Bottom line: To get the best fare check out several sources (on-line and in person) if you have time.