Let me clarify this in a few points, because point forms are easy on the eyes:Annoying since one is used to not having to care about regions when buying games for the NDS. I think they should have made it like the PSP games, where games are region free and media like movies and music are region locked.
- Yes, you can run American DS games like Diner Dash on your new Japanese Nintendo DSi
- No, you cannot run an American DSi game on your new Japanese Nintendo DSi
- No, you cannot run Doki Doki Majo Shinpan 3: Snapshot Lecher Edition (a possible game for the DSi) on your American Nintendo DSi
- No, you cannot run a downloaded Rhythm Tengoku (probably from the soon-to-come GBA download service) onto your American Nintendo DSi
- No, you cannot run future emulators and ROMs you don't own using your newly-acquired 4GB SD card on your new Nintendo DSi. Technically, you can, but that's just criminal and many shades of wrong