I'm importing a DS next month (I'm in Scotland) without a doubt. If Mario 64 was the only game ever released for it, I'd still be in there. I love that game so much and to have it on the move, with extra stuff, is just class. However, it isn't and with Castlevania, Winning Eleven, Final Fantasy, a new Seiken Densetsu, Mr Driller, Advance Wars and a whole lot of other stuff on the way, DS is a sealed deal.
Since the PSP launch is a little further away, I am less enthusiastic because less information is known. I'd be a little reluctant to pay in the 300 range for a handheld but if they launch with some good games then I'll take a look. I have a feeling that PSP might be the brunt of more ports and unoriginal titles that the DS though, but to have a portable MGS and GTA is no bad thing.