I’ve just got a quick $0.02 worth to add. Just from observation, when people are unaware of the source of information, they use clues to attempt to distinguish good sources from bad ones. Good grammar, while it does not necessarily correlate with knowledge on any particular subject, is often seen at least as a hallmark of a good education, if not of intelligence – especially by other people who also use good grammar (such as employers, customers, and hot little undergrad English majors whom you’re attempting to impress).
You can protest all you want about how fair or unfair it is for people to judge what you have to say based on how you say it, but the bottom line is that they do it. You can either say, "Fuck 'em" and not care, or you can attempt to use proper grammar and avoid the misrepresentation of your intelligence and/or attention to detail in your thought process that improper grammar has the tendency to convey. However, if you choose the "Fuck 'em" route, don't get all pissy when people discount what you have to say. After all, you don't care about them anyway, right?
I'm probably overly sensitive to grammar in the written word because for one, law professors are REALLY anal about grammar, even the grammar no one else in the whole world remembers (like gerund rules), and two, because I have to teach the stuff to earn beer money. So, take my opinion with a grain of salt.
My addendum to the grammar watch-list: Anyone, everyone, none, no one, and all such "one" pronouns are singular, and thus cannot be used in conjunction with the "their" possessive pronoun; e.g. "Did anyone lose their watch?" is incorrect. (It should be "Did anyone lose his watch?"; or, for the politically correct, "Did anyone lose his or her watch?").
(BTW, TEK, how do you get the moderator to include your paragraph separations? Mine always get jumbled into one giant rambling paragraph).
NOTE FROM MOD: IT TAKES A LITTLE PROGRAMMING KNOWLEDGE. SOME READERS KNOW IT ALREADY AND ADD IT THEMSELVES. SOMETIMES THE MODS ADD IT IF THEY HAVE TIME. MOST OF THE TIME WE DON'T DUE TO THE VOLUME OF POSTS.