Yeah, I'm guilty of leaving my truck running at times 2 hours while somewhere. I live in Phoenix and the temperature gets... well, you know. I also routinely start the truck in front of the house to cool it off for pretty long amounts of time. I also remove the key fob.
I only do this in the summertime because it's so damn hot. I figure diesel vehicles sip fuel when ideling at least relative to a gas engine because gas engines run at a constant air/fuel mixture even when ideling... Also, since it's so damn hot, my engine stays at normal temperature and my post turbo temperature never gets below 325-350. In this heat, even when I start my truck "cold" in front of the house my EGT heats up very very quickly. It's my theory that as long as my EGT's are up and the engine temperature is up I'm not risking any blow by/oil contamination.
Mike