I'm an American ex-pat living in Tokyo. For me, a trip to work or a trip to the in-laws or a trip basically anywhere on the train or subway very easily fills up my maximum 10 hits with new contacts. I have over 1000 at this point, and I don't very often take my 3DS out with me.
I'm on a rare trip home to the US now, and I got all of one hit during my four-hour layover in San Francisco, nothing in the Chicago Airport, nothing in Atlanta. Needless to say, no hits in semi-rural Georgia.
So is Street Pass pretty useless for most people?
For me, yeah pretty much. Very frustrating that Nintendo put those purple pieces in some of the puzzles that can only be obtained via streetpass. I've had my 3DS since just after launch and have gotten less than a dozen distinct streetpass connections.
I lived in Japan for a couple years in the 90's ... I often think about how great the streetpass thing must be there. You confirmed my suspicions, you bastard.
I've completed all the puzzles. I finish them almost as soon as I get them.
It's kind of fun getting contacts from different prefectures in Japan -- I have maybe 30 or so now.
It's a great concept. But there seems to be a huge range for how successfully this thing works, and I have no idea how it could be improved. It's a concept designed by someone living in a major, crowded Japanese metropolis, though, obviously.