Just flew JetBlue a few days ago as an EXP. When I booked, the JetBlue site wouldn't take my Advantage number, so I added it via text chat (which is very good). At the airport, I checked in at the counter and they didn't charge for bags and upgraded us to emergency row seats which normally would have been $100 each. Upgrading isn't available in advance. The boarding pass said AAElite which also gave us priority boarding and presumably security, though we have TSA Pre.

It's a great partnership as far as I'm concerned.