Flying several itins on AS domestic recently. When booking award tickets, as demanded I used my real first name as the traveler, as opposed to the middle name I use for everything else: common speech, AS Mileage Plan account, credit cards, etc. As a result, I wasn't able to use online checkin for either me or my wife (same PNR), and we had to do this at the airport. Seat change capability suffered, and we had to arrive a little earlier.

Lesson: put middle name in the "first name" box. Leave middle name blank. My identification shows all three names in full, so there shouldn't be a problem at the TSA checkpoint. Anyone with experience to the contrary, please weigh in.