One minor point for the curious..
From my market (Stockholm) I can book both AA and BA on code-share flights; AA tends to be slightly cheaper even on BA metal.
Another advantage is that I can book seats right away on the BA operated flights from the AA web site. I have a BAEC Sliver card, so I would be able to do this on BA.com as well. However, it negates the BA extra £60 for none-status members.
Please note, I have only researched this so far, not made a final booking