what are the three DS coins, and what kind of things can you do with them. Sounds like an interesting incentive to keep the 3DS on you and go for a long walk! XD
There aren't three DS coins, it's 3DS coins . They're called "play coins." They are used for the built in games and some other games, e.g. in Street Fighter you can unlock little figures for a sort of trading/streetpass minigame. It isn't really an incentive for a long walk, since you max out at 10 coins (1000 steps, not quite half a mile) per day; Street Pass is more of an incentive (connect to nearby 3DSs) but it's pretty uncommon for me to meet people except in certain places like GameStop. I still take it with me a lot of places though.