I was able to do very limited bits of what Tammet talk's about at some point, i can certainly understand what hes saying.
Not the math bit, or anything particularly usefull, but just "getting" certain information, with zero conscious thought process.
Uh, i dont know what else to say about that really.
I recall a kid, very autistic, maybe not so much a math whiz-but he memorized some 5000 numberplates , of passing cars, at school.
Often, he wouldnt see them again for years, but when he saw the car, (still out of veiw for us to read the plate) passing by, he'd recite the plate, the car model, identifying features and the date, (often years before) he saw it last.
With a speculative commentary of where he thought they might have travelled to, given the timeing and load etc. I think that was the part he was interested in.
Thats full on.