The Apple is a site "where teachers meet and learn". It has a page where teachers can supposedly learn from "11 Grammar Mistakes to Avoid". And guess what: as Steve Jones has pointed out to Language Log, not a single one of these alleged grammar mistakes is both (a) genuinely relevant to English grammar and (b) actually a mistake. It is truly extraordinary what garbage teachers are exposed to when it comes to matters of how to describe what is and what is not grammatical in Standard English.
I suppose I have to go through all eleven of the misbegotten peeves and fumbled explanations that this execrable site provides. Here goes:
1. The page presenting the first alleged mistake is headed "Constipated Clauses", and the advice is that you should never use "it goes without saying" or the adverb "obviously". This has nothing to do with grammar; it is about trying to direct people in the matter of what they should say, not of what form of words is permissible for saying it.
2. The second is headed "Comma Vomit", and recommends against certain uses of commas. In fact it recommends against the comma use in my previous sentence, and against the comma in this one. There's a lot of variation of choice in comma use among expert users of Standard English, and it certainly cannot be claimed that "Commas should only precede and, but, for, or, nor, so, or yet when they introduce an independent clause". Do not trust this page.
3. The third is headed "The Death of Adverbs", and says that adjectives modify nouns and adverbs modify verbs. As it happens, a new paper (by John Payne, Rodney Huddleston and Geoffrey K. Pullum, forthcoming in the journal Word Structure) shows this is actually not always true. But never mind the wider picture: what the page is telling you is that I can do that easy is wrong and should be corrected to I can do that easily. This is a style difference. Most American speakers will say they can do it easy when speaking in relaxed and casual mode, and most will agree that "do it easily" sounds more careful and formal. As an observation about formality levels, this might be worth making; but it doesn't amount to an error in syntax.
4. The fourth is headed "Less vs. Fewer", and warns against substituting less for fewer. It is claimed that the latter "describes finite, listable items". Strictly that would imply that it's ungrammatical to say There are fewer rational numbers than reals, because neither the rationals nor the reals are finite in number, and the reals are not even listable. But never mind the math. The page recommends saying "fewer brains", as in "He has fewer brains than I thought", which is ludicrous (how many more does he need, if he has one?). It's an old, old usage quibble, and here it's very badly presented and described.
5. The fifth says you shouldn't reduplicate "etc." — it doesn't say why, but merely alleges that if you write "etc. etc." it will show that you don't know what you're talking about. This is just a style peeve. It also says you shouldn't confuse it with "et al.", which is a purely lexical point.
6. The sixth (oddly headed Prevarication Junction) tells you not to use "I think" or "studies show". Again, this is being bossy about what you should say, and has nothing at all to do with what it is grammatical to say.
7. Number 7 distinguishes the words affect and effect in their noun and verb uses. You can look them up in a dictionary. Purely lexical information, no grammar.
8. Number 8 is also purely lexical, or even just a spelling point: it distinguishes than and then.
9. Number 9 actually is about grammar, but what the page says is not true. It asserts that none "is always singular" for purposes of verb agreement. This just isn't true for Standard English. When none is a subject, the agreement is often plural (are, for instance). None of us are perfect, says the Reverend Dr. Chasuble in Oscar Wilde's The Importance of Being Earnest. Wilde was not intending to portray Dr. Chasuble as incapable of speaking correct English. The myth that none takes only singular agreement on the verb lives on despite many refutations. Serious handbooks of grammar and style don't represent it as ungrammatical. (Of course, the idiots Strunk and White do in their clueless book The Elements of Style; but they get almost everything wrong.)
10. With number 10 we are back to Latin abbreviations: "i.e.", it tells us, is different from "e.g." — and so it is, but this is not grammar.
11. Finally, alleged mistake number 11: writing could of for could've or could have. A spelling point, really; nothing to do with grammar. A guy who writes I could of been a contender can't spell, sure, he knows how to say grammatically that he could've been a contender (and who knows, perhaps in some realm other than writing he could've been).
That's it. There is nothing more. The Apple has nothing for you but unmotivated content bossiness, unacknowledged style preferences, familiar lexical distinctions, and inaccurate punctuation guidance. There is only one clearly grammatical point, and it makes a clearly false claim about verb agreement in English and misinforms the user badly.
If this pathetic parade really the best that The Apple could provide for the teachers who turn to it, then I can only say that my previous blasts at the idiocies of the burgeoning industry of uninformed grammar punditry must have been far too understated or far too little noticed.