Tonight I spent the night at what I shall now dub the "San Francisco Airport hotel suites". I was in between flights — I arrived here from Vancouver at about 8pm tonight, and my flight the next morning to Miami boarded at about 6am — so I didn't want to bother finding a place to stay for the night, or even to bother leaving the airport and coming back again so soon. So I found what seems to be the unofficial place to spend the night at SFO.
Comfy couches, reasonably dark and quiet: perfect place to sleep.
This little area is a café eatery place, just one level up from the departures floor in Terminal 2. Most of the cafés start closing at about 11pm, and from then on, people start coming in and finding a couch to sleep on for the night. Each booth becomes someone's little "bedroom". The place is outside the security checkpoints, so anyone can wander in — but I think that the security come around sometimes, and check that there aren't (too many) homeless people exploiting the airport comfort.
I managed to get about 4 hours of sleep here, which wasn't too bad at all, considering the lighting, the other people around, and the intermittent PA announcements. I wouldn't exactly recommend this as a place to stay in SF; but hey, if you're stuck between flights for one night, it's certainly better than nothing.