Today i went to GAME and one of the guys there called me over and let me have a go on a 3DS (woot) so i took the time to ask about if DS's still play foreign games due to something i'd heard about the 3DS. Apparently nintendo are now adding something to new DS games to make it impossible to play them on foreign consoles, but it's only on games made after a certain date (which i don't know) so i asked about PSP's, the games do a software update (or consoles if you get software updates online) which will stop you playing foreign games. So, if you want to play japanese games in the UK, you may need to buy a japanese console or hack you own.
Anyway, i remembered after i got home that i have an american 2nd hand DS Lite, so i'm gonna question the guy at game again later and find out if this import prevention thing would effect it, then try any new games (pokemon black/white or okamiden) on it and see if they work (they better bloody work)
(i've asked on facebook so now i'm hoping to get more info)
EDIT:
Info found by Mr Fiddles