I once had near perfect written English skills, I actually started out my life intent on becoming a journalist. Even in the days of BBS' where abbreviations were frequently used to save money on telephone costs I refused to leet my written messages after the obligatory "hi m8".
Then I lost the ability to write in an incident when I suffered some brain damage. I could write words but not sentences, it is not an easy thing to explain but basically I had to learn again. I can still get words muddled but I think now I'm atleast up there with non native speakers who - to coin a phrase from this thread - "put the effort in".
What the experience taught me is that the most important aspect of communication is to be understood, it is not a demonstration of my adeptness at the written word, nor is it a measure of my intellect. Communication is particularly just a tool to exchange a thought, idea or to express ourselves.
Anyone who treats language any other way by judging others written abilities is still doing just that except the message they are conveying is not as clear, specifically the act of being a "spelling Nazi" is a form of expressionism, and demonstrates ones anal retentativesness.
Expression is an important concept too, in MSN with some people I'll often totally change my written style to a less formal one, using spellings such as "sommit" instead of "something", as a means of expressing a more casual tone.
As far as I am concerned the biggest culprit in cases of corrected spelling on forums is usually the correctee, I say usually because some muppets really dont get their message across when posting, which defeats the purpose of wtitting anything in the first place.