Mostly I ignore it unless someone is so horribly unintelligible that I can't figure out what the hell they are trying to say. The people who obviously know better but still go ahead and use terrible grammar, spelling and sentence structure anyway, though, are just lazy regardless of whether the medium is just a message board or not. A spelling mistake or misusing a word here or there happens to everyone, so that's not anything to bash someone over. However, the folks that seem to have some sort of superiority complex and are going out of their way to call other people stupid in one fashion or another while simultaneously butchering the English language are practically begging to be ridiculed.
jag