Grammar, do you like a person who speaks well, with good grammar? Why?

Of course. It shows intelligence and education.

Well, usually you can't detect grammar when it's being spoken, but if someone says something like "I seen" (as opposed to "I saw"), well, that does give me aural clues about the person, and they aren't positive clues. ("Does this person live in a trailer park?")

Easier to interpret with less likelihood of misunderstanding.

I like a person who is extremely articulate, it shows focus. It also shows a sign that the person is goal oriented and has goals.

Hmmm, interesting question... I'll ask Greta for her opinion on the matter... Greta? Do you like... What? Mr. Snozzle? What about him? Ah, I see. Poor little fellow, always getting himself into mishaps... I'll get back to you later.