Just take your DS/DSi to the GameStop, use Mystery Gift (I presume), and you can get your Pikachu colored Pichu! Which, when traded to HG/SS, unlocks a special event at Ilex Forest with the Notch-Eared Pichu!
Sure, it's just a few Pichu's, but hey, they're rare!
And most importantly!
Tell your Gamestop employees that you accessed the event so they can mark it down! I know an employee who said that they are supposed to put a mark down for any who participate in the event, but they have to know. If Nintendo is disappointed with the total amount, they could potentially stop doing these events; which would stink.
So; has anyone picked it up yet? Seems like a nice thing to do while pre-ordering HG/SS, right? Couldn't hurt anything.