[SWTXBelle]

I don't believe a command of grammar has anything to do with social class. There are numerous examples in public life of those who may technically be of a high social class who cause their former English teachers to weep. It does indicate a certain level of education, but is easily learned by anyone who cares to go to the public library. (I wish I could say anyone who has received a public education, but we all know that is no longer the case. I know of a school district where you can be fired for teaching sentence diagramming!)
Anyone who has tried to make sense of a post filled with grammatical errors or had to try and translate the pigeon English of a technical support person knows that it is frustrating.
I do believe it is necessary for clear communication. With the advent of text-driven technology it has become more important than ever. That said, I am not one to go around correcting grammar for free. Heck, I've made a fair living doing it for money. Of course, if you decide to adopt a holier-than-thou attitude here on GC and do so in a post riddled with errors, you have painted a target on yourself.
I also think it is important to realize that a language is not a static thing. It evolves and changes. For example, technically "their" is plural. But having dealt with the "his/her" thing for so long, I have come to think that perhaps a nice, simple singular use of "their" would make things easier. Which is better - "Every student must bring his/her book" or "Every student must bring their book". I know the second is wrong - but I hate the first. Mind you, I still use the first. But secretly, I hope the second is eventually accepted.