Not a grammar Nazi; but, like it or not...people will judge you by your grammar.
For simple posting on a message board, I don't let other's bad grammar get to me too much...I know when I'm at work, I have to jump on and sneak posts here and there and I let something slip every once in a while...however, when I read posts of letters and emails that people have sent to Congressmen, Senators, letters to the editor, and complaint letters to businesses and corporations, etc...and the writer couldn't tell you the difference in usage between "there," "their," and "they're" or "your" and "you're," "then" and "than," "accept" or "except," "to" and "too," or "affect" and "effect"....to save his or her life, they shouldn't wonder why they don't get their desired result. When managers and Human Resources personnel are reading a resume`, all they have to form an opinion of that person is that piece of paper. As soon as they get to a typo or improper word usage...they have their opinion and that resume` will be promptly round-filed. Customer Service and Public Relations personnel work the same way. They may not throw the letter or email away...but, rest assured, they've formed their opinion and all their dealings with the individual that wrote it will be colored by their, "this guy's an idiot," opinion.
I'm reading through a study guide for a certification test I have to take in the next month. A published book that was looked over by the two writers and more than likely at least a couple of editors before going to press...I'm on chapter 8 of 12 and already have a list of 27 errors, to send to the publisher and say, "Hey, you may want to fix these..."