The folks at DNA Lounge recently took over Bowser's next door and have converted it into a 24-hour pizza place. The prices are definitely among the highest among its competition (slice of cheese is 4$), but it's not so bad if you can split a pizza, and i realize that they need to have higher margins to remain open 24 hours. The slice isn't as good as what I've had in New York, but it's definitely one of the better ones in SF. They also have $2 off from 11-4 and $1 off from 4-7. Ingredients also seem to be of pretty good quality, and they even have other things like espresso and sandwiches.
When I went on Saturday night it seemed like the late hours were mostly to provide a place for people in the nightlife industry to eat after they get off work, although it does make me wonder what (if any) business this place does earlier in the week when there's not as much nightlife.
I also loved the interior, as they've made it into a tribute to the DNA Lounge, with posters covering the walls of seemingly every event they've had there.
As I said, it's not by any means a destination pizza spot, but it's nice to finally have a 24-hour option in SF that's not a diner, fast food, or donut shop.