I'm planning a mileage run LHR-SFO-LHR, I'd land in SFO around 13.00 and the flight back is around 18.00.

What do I put on the green card as my temporary residency address for the 4 hours? What on earth will the immigration officer think of my trip? I had real hassle last time I flew into the USA, even though I was staying 4 weeks on vacation. They always seem to single me out...

I had a similar problem flying from HAM (Bermuda) to LHR via JFK, I landed into JFK at 13:00 and the flight to LHR wasn`t untill 22:00 so I decided to go into the city for the afternoon, I put down the address of the Waldorf Astoria hotel in New York, and said I was here on vacation and was leaving the next day.

I have been into the U.S about 14 times now and the only questions I have been asked are Where are you staying (one location or touring)? Are you here on business or vacation? How long do you intend to stay?
I haven`t ever been asked to produce evidence of my return ticket, after all you may have an open ended or flexible ticket (as long as you leave within 90days under the visa waiver program) and as far as I am aware your first night`s stay needn`t be pre-booked, again I have never been asked to provide actual evidence of a confirmed hotel reservation.

Believe me, you will not be the first mileage runner than an immigration officer has met...

When I did this in the past, I just put in the airport name where I was doing the turn.... I would never take the risk of "lying" on a form.

William

Absolutely! SFO is your temporary residence. You might even try to engage the immigration officer in a discussion which will cause hm to lose interest and move you right along.

In my travels, when I go through immigration at a point where I am planning to spend a few hours before flying onward (although typically not back to my origin), I will write "transit" in the form where it asks for my local address. I have never done that in the US, so I don't know if this would be appropriate advice for the OP. My guess is that it might be at least as appropriate as writing "SFO" on the form.

I do, however, like gre's advice of engaging the officer in a discussion that will cause him/her to want to be rid of you quickly.