damn you Onshi! You got me there, Fight Club is full of crap too, even moreso than Memento. Still, I find the characters and story much more compelling in that one than in Memento.
As for your question, there are several times in the film where he states "I don't have amnesia. I just can't make new memories." Well, apparently he couldn't make a new memory about anteriograde amnesia existing, since that's clearly what he has.
by and large though Mun, i think you're right. it's not a bad film, i just didn't like it...
another movie recommendation (to stay on topic):
Wayne's World. I think it's Mike Myers' funniest film ever, way above Austin Powers