I just got my system and even though I live in New York and it's Summer getting a Street Pass is not as easy as it seems, though it's not as scarce as some other people have been reporting.
Yeah, it's definitely not a daily thing, but I've had mine since launch and I've got around 20 streetpasses, with about 15 of them "natural" (i.e. totally random people at non-game events). 5 are just friends that I intentionally met because I knew they had 3DS's. To be honest, more than streetpassing people you know, the natural streetpasses are the most awesome. I've gotten some at the mall, one I got at a Dodger game, another I got at Disneyland literally 2 days after launch.
The funniest thing that's happened so far was at the technical rehearsal for my daughter's ballet recital a month ago. I was in the theater, waiting for my daughter's class to get out of their green rooms and onto stage, when I saw some 10-ish year old kid a few rows down playing with a 3DS. Now, ignore the fact that that kid's parent bought them a $250 toy. A 10 year old. Whatever. I immediately checked my 3DS, which was in my messenger bag, and I noticed I wasn't getting a streetpass. What the hell. The kid was literally 12 feet away. Then I noticed that the kid's wireless light (orange, bottom panel, top near the hinge) was off. I was willing to bet that this stupid kid didn't even know how to use their 3DS and probably didn't have streetpass set up or turned on. Pretty frustrating. I really wanted to walk down and teach them how to turn on their streetpass, but...well, non-gamers would probably view a 32 year old man walking up to a totally random kid to get them to mess with their game console as just a little creepy, bordering on pervy.