Tried out the StreetPass function yesterday and managed to score four Mii's inside an EB Games, perhaps not surprisingly. Got another three at lunch time today - all of whom where female (possibly not IRL). TIP: Before you start cruising with StreetPass, you need to play the Puzzle and Quest games at least once. The new Mii's won't show up in those games otherwise.
Note the grey-haired Mii second from the right. I smiled when he introduced himself as our ex-Prime Minister.