DON'T REGISTER YET
But aside from that, you may be curious, what IS Club Nintendo?
For the United States and select other regions that have not had it before, it's a Loyalty program based on product registrations that offers you cold, hard gifts for your Nintendo purchases.
Now according to all the wording that has popped up in the preliminary site, it looks like there may be some kind of retro-activity with Wii and DS game registrations that will occur. For now, though, they're definitely not ready, and even when I registered a few minutes ago, it didn't show anything registered (even though I linked it to my My Nintendo account which has, like, 50-75+ registrations, though not all DS or Wii).
So don't sign up just yet, but soon, Nintendo should make an official announcement and you can save up for some neat prizes.