spelling/word usage mistakes don't squick me, but they seem to have an effect on how seriously I consider the actual meaningful content of the words i'm reading.

This is just the way i operate by default. If i somehow already know the person is really intelligent and just happens to suck at typing, of course that would change my perception. I also seem to be able to cut ESL people a lot of slack too (which is good considering how advanced *my* second and third language spelling and grammar are ).