If I may contribute once again to the off-topic side of this conversation, Raffles is right; I'm not an insanely picky scholar, but I do care about spelling and grammar. However, I don't care about these things simply for the purpose of needling people; I'm interested (on an amateur level) in the English language and its history. I like finding out information about the origin of a particular word or phrase, especially one that I've used for ages without really thinking about it. (
WordOrigins.org is an excellent website for this sort of thing, if I'm not the only one.) An appreciation for correct spelling and grammar goes along with that interest.
I also agree with Raffles' other point: communication is a necessary part of life for social creatures (which we are), and a solid grasp of the mechanics of your language will help you to be an effective communicator.
One more note: I have a great deal of respect for those of you who speak English as a second (or third or fourth or...) language. It's the only one I speak, so if I ever make a derogatory remark about your skills with the language, feel free to put me in my place.