Returning from Hong Kong after a week's business trip:
Officer said "Good evening" (then swiped passport and green card, and stamped passport ARC). Less than a minute later, handed both back to me and said "Thank you". No questions or discussion, not even asked how long I was away.
When I passed the customs desk, the officer just said "Welcome home" in a friendly tone.
It seems to me like the SFO officers have had some kind of training in people skills, but I could be wrong. It might have just been a fluke, or the fact the load was light (ours was the only international flight in the hall at that point in time.)