Basically, when you walk past someone else with a 3DS, you get a StreetPass hit, so your 3DSs share data automatically. For example, in Heroes of Ruin, if you StreetPass with someone who has the game, some of the items they sell will start appearing for you to buy in-game.
That's why I have so few StreetPass hits, because barely anyone where I live has a 3DS. :P
And yep, I assume so. ;)
Also, I can't find your 3DS friend code anywhere... am I just not looking hard enough? xD