I'm not convinced Blowfish has the absolute best sushi in San Francisco, but for overall dining / people-watching / scene-making experience, I give it a strong thumbs-up.
Located in the once-bustling Multimedia Gulch, Blowfish was an early outpost of style in an otherwise quiet / industrial neighborhood. With its aggressively modern design (sleek steel plate benches, plain blond wood tables, Anime videos running on video monitors), stylish waitstaff and of-the-moment (e.g., international electronica) background music, it was (and is) a magnet for young hipsters from Potrero, the Mission and Bernal Heights.
As for the fish, Blowfish consistently delivers good quality, in more or less traditional presentations. No sushi nouveau here (e.g., jalapeno slivers, etc.), and no obsessive attention to the latest, most obscure fresh-off-the-boat cuts of fish. But what you get will be fresh, of excellent quality, generously cut and carefully served.
In addition to quality fish and high style, Blowfish offers an excellent weekend (Thursday through Saturday) drink & schmooze scene - the cosmopolitans are (hopefully) a thing of the past, but you can count on a strong showing from the young & stylish set, which makes for fun people-watching for those of us no longer in that phase of life. Give it a try and let me know what you think!