I don't know if this is helpful, but I not only obsess over spelling and punctuation, I obsess over definition as well. In other words, if I'm not sure that I know exactly what a word means, I look it up first. I've even gone back and edited my posts on numerous occasions just because I thought of a better way to word something after posting. I also felt very sick to my stomach when a history teacher spoke of the the Imperial diet (pronounced dee-et), but mispronounced it as diet (dye-it). However, I didn't correct her because she was the teacher, and I felt that I didn't have the authority to do so.
In a similar vein, I once felt irritated when a friend of mine sent me a private message referring to a previous private message as an e-mail. So irritated in fact that I actually typed a description of how the forum's private messages worked, and how e-mail worked, and carefully explained why they weren't synonymous. But then I decided not to send it for fear of eliciting offense. (Although later on when I found out they weren't easily offended by such things, I went ahead and sent it.)
So, I'm probably the worst about this, for what it's worth.