Grammar does matter to me, but that depends on the source. If it's one particular friend of mine (we'll call he "Alex") and she has a very high level of grammar comprehension and a fantastic grasp of the English language, then when she makes a typo or an error I tend to point it out (unless she does first, which is usually the case.) Same thing if I'm talking to a writer. I expect good grammar and an extensive vocab.
However, if I'm talking to a different friend - Sam - then I don't worry about it too much and I don't make an effort to use complex vocabulary because she doesn't know quite as many words and generally doesn't text me with correct grammar (or punctuation, for that matter.)
Just depends on the source.