The Good: For JAL, access via additional codeshares to a huge U.S. domestic route system, and for their top tier customers, access to the AAdmirals Clubs in major airports.
For AA: Access via additional codeshares to most of the Far East without having to fly there ourselves.
The Bad: For JAL, not much.
For AA: Access to the Far East without having to fly there ourselves. (From a flight attendant perspective.) Seriously, this reduces the need for AA to invest in Far East expansion at this time.
I think JAL joining ONEWORLD is GREAT. JAL is a quality airline with great traditions, why did it take them so long to join? Since Cathay is the only other airline within the group in Asia, JAL is a great addition. ONEWORLD needs something in China, perhaps, China Eastern in Shanghai.
JAL has been a flying 747's since before SINGAPORE Airlines placed its first order for 2 in 1973( Singapore is a great airine too). JAL, like many ONEWORLD airlines has operated fleets with primarily Boeing aircraft including the new 777-300ER and soon the 787. I hope JAL will fly the 747-8 as well. Cathay, Jal & British Airways have been rumored to want Boeing to build the 747-8, so Boeing is, finally.
JAL's route system serves many cities where ONEWORLD airlines have hubs or a major presence. It serves London-Heathrow with its "Big Ben" Express service as well as JFK with its "Big Apple" Express featuring the newest airplanes and the most updated First and Business Class seats. Chicago is important since AA hubs there. Cailfornia has always been special to JAL as San Francisco was its first US city, Los Angeles is JAL's most frequently served US mainland point. Honolulu, Hawaii with the Japanesse honeymooners is the one city served from most major Japanesse cities, Jalways( a JAL Subsidiary) flies most of these routes with denser seating then a "Big Ben or Big Apple" airplane.
The Capitals of Europe, Paris, Frankfurt, Amsterdam and Heathrow have long been in the Jal portfolio. Australia is a major Jal golf and vacation destination with service to Brisbane and Sydney. Sao Paulo has been the only city served by Jal in South America for years, they fly Nrt-JFK-GRU with a 747-400. Jal has an extensive portfolio of Asian destinations. JAL's service to America has always been underserved, why not fly to Miami or Boston, I think these two cities would welcome it with open arms.