I just did the calssic mileage run on an AONE3 RTW ticket travelling LHR-IST-LHR yesterday. BA.COM could not check me in online as "my ticket was not validated" even though it was issued by BA and validated at BA at Heathrow with a sticker, I checked in and the agent issued me both onward and return boarding passes. Enjoyed served breakfast at Terminal 1 First lounge (Which is definitely better than the Terminal 4 Concorde lounge)
Smooth flight IST except for the terrible club world seats Shame BA. These seats need to be dumped and replaced.
Landed in IST just breezed through sign marked Transit (No visa no fees and no security) The security guy at the gate nodded at me I nodded at him and went to the departure area. Didnt ask for my boarding card or passport refreshingly different from US.
IST is as good as SIN for shopping and better than DXB. The BA terrraces Lounge is excellent with REALLY GOOD CAPPUCINO AND LOTS OF YUMMY EATS. Admiral club note.
Flight was announced, walked to the gate, easy security (Much much better than any US airport) and flight returned to LHR 30 minutes early. Truly enjoyed the experience.
IST airport is indeed very good and the BEST airport for a turn around even better than SIN and DXB. Totally hassle free and a shopper's heaven