Pokemon Platinum is a game worth picking up if you know Japanese or if you have the mechanics of Pokemon so memorized you don't need to read it. It's a bit pricey to import PP, and people all know it'll be coming to the States eventually with some changes to reflect things that can't be done here that were done in Japan (Such as the lack of a theatrical release of the Shaymin film). If you know how to use your DS correctly and have a basic knowledge of Japanese, you can still get the Secret Key and various other objects to help you complete your Pokedex and take full advantage of this game.
Diehard GameFAN's suggestion is wait for the North American release, and join in with the millions around the world that will enjoy this game at that time. For those of you who can read Japanese, there's no reason not to import this as Pokemon Platinum is easily one of the best RPG's released this decade.