Well, my DH is HG+, the smartest person I've ever met, and dyslexic. He makes a lot of the kinds of mistakes you describe, and not due to carelessness. So no, I wouldn't judge based on that. I also wouldn't judge based on grammar, as I think it is perfectly possible to be very intelligent and yet grow up in/be a part of a culture in which grammar is very different from mainstream/academic grammar. I think to some extent you can judge based on content, but even so it only speaks to how well that person has communicated his or her thoughts on that one particular day (and how well you have read and understood).
I'll also point out that there are plenty of kids who are HG/PG whose parents are not. DH & I both have ND/MG parents, yet we are both on the very upper end of the curve.
Gratefulmom, the reading level thing bugs me too, though I'm sure I was once one of those people (and maybe I still am, since DD has not taken and is not likely to ever take a school reading test). But then, I often find that the things that bother me most about other people are the things I dislike in myself.
