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

I take it the OP was on the morning flight to IST, operated by a 767. Are the J seats on the evening flight, a 320, any better?

Not really. They are essentially the same convertable seats. Your best bet is to get a seat on the left side, because they condense the three-seat row into to two seats, giving you your own armrest and a little storage space between the seats. The right hand seats are extended oout so, evne though there are three seats, they are as wide as the left, but you share armrests and lose the storage space.

For my money, bulkhead seats ar ethe way to go on these flights.

I flew the 767. TwoXtwoXTwo configuration. The middle row had that extra bit in the center. The problem was the very limited recline and the poor leg room. When you reclined to sleep on the longish flight the passenger in the back correctly objected. Entertainment was on a ceiling mounted 12" TV. The setas were hard and the headrest could not be adjusted.It brought memories of AA's 757 first class seats

I'd avoid the bulkhead on the 767 - it is tighter than the Airbus. The centre pair are the seats to choose as the window pairs expand by no more than half an inch. The AC seats on the Airbus are the most comfortable of the lot, but frankly CE seats are rubbish for a longish sector like IST.

Oh, and generally the 767 cabins are a bit tatty.

I thought the CE A/C seats on the IST-LHR A320 were more comfortable than AA's 757 F seats, which are used on much longer segments. Actually on a 4+ hr segment last weekend on an AA MD80 in F I was struck at how vastly more comfortable the CE seats were, never mind the service. The CE chairs on IST-LHR may not be the world's greatest J seats, but they're a far cry from the worst.

I'm bringing this back up because we'll be doing a same-day turnaround at IST next month, the incoming segment the last of our RTW, the outgoing on a self-bought (non-RTW ticket.) Can we get the return BPs at LHR in the morning, or can we get them at the Terraces lounge at IST, or do we need to go through immigration (hope not.) Probably won't be able to use OLCI the day/night before as we'll be coming in from TLV.

I'd be interested to see what others say about this, methinks BA would consider this use of back to back tickets and therefore won't issue return BPs.

I'm curious too, but about the above "back to back" comment; why would BA object to it? there's nothing irregular about it, right? or is there? I know that in a similar situation IB would have no problem issuing the BP in MAD for a same day turnaround flight to MAD.

Experience has taught me that BA do seem to be funny about a point-to-point journey issued on two separate tickets, that's what I meant.

Wow. Perhaps padding and seat structure aside, the AA seats (757/MD) are superior to the BA CE seats in just about every quantiative measure -- pitch (38" vs. 34"), width (21"/19.5" vs. 19"?), separation from neighbor (a "real" armrest console on AA, particularly if you're not in the A/C side of a BA narrowbody or the center seats of a 767), and perhaps an overlooked measure, seat cushion depth, front-to-back (don't have stats, but BA CE seats are still COACH seats). I would take an AA domestic F seat over BA CE anyday, and I'd even "suffer" the AA service on a longer flight vs. sitting in BA CE if it was a choice (which of course it's not, so this is all theoretical...).
But to each his own.