That's a tough one to call. The Japanese in Japan are polite enough such that even if you were 'acquaintances' with a Japanese person, you'd rarely know that you were 'nothing' to them. But thats a gaijin perspective of course. I had a few neighbours who took an interest in me in Kanagawa, and they always stopped to say hi if I did, otherwise we'd pass each other but still acknowledge each other at least with a wave or nod. The only time I ever really received a cold shouler was when I'd pass a student on the street who'd gotten it into their head that NOVA teachers and students speaking ouside of school = immediate death or something.

Here in Toronto, the young Japanese crowd (recent grads, world travellers) all seem very eager to chat and meet again, but they probably aren't representative of Japanese culture at large.