I can't write with my left hand. I try occasionally, and can't. I even practiced once, just to see. I don't like cutting with my left hand either, and I've never tried to learn.
But I nonetheless use my left hand quite a bit, more than a lot of other people I know. Yet I've never considered myself really ambidextrous.
However, there is one high-level activity most people do with their second hand: wiping their asses. Some scientists speculate that this is the actual origin of one-handedness; i.e. those of our ancestors who got the genetic predisposition to touch food etc. with their clean hands got sick less often and had more offspring... *Lunatic*, n. One whose delusions are out of fashion.
