It's already been discussed, but this is a good time to repeat:

If you are savvy, you should get miles for BOTH airlines.

That airlines you are rebooked on will credit your miles automatically - if you don't already have a membership number, get one at the counter.

As AnneS correctly pointed out, the airline that you were originally booked on will grant you miles for that segment if you send them a copy of your original ticket + boarding passes. I've generally enclosed a brief note and the credit has shown up quite quickly (3-4 weeks)

I realize that it's not worth the terrible inconvenience but a silver lining nevertheless for all you AA flyers.

[This message has been edited by megamiles (edited 02-08-99).]