Example: We have the infamous "do not end your sentences with prepositions". And why did this ever get to be a rule written in the proverbial linguistic stone? Because English grammarians were having Latin-envy. In Latin you can't end with a preposition. Why? Often, it's because the preposition in English is really marking things like dative case for the indirect object of the sentence. And in Latin, that was a case marking on the verb - you can't leave the preposition at the end because there was no actual preposition. Just a noun with a case ending. End of story. You move the noun, you've moved the implicit case marking - and thus the "English preposition".
But English isn't like that. We use prepositions which are, in fact, separate bits of morphology. They're in the lexicon as separate entries. They are not just endings on the noun. Thus, we can strand them at the end of sentences with impunity. Is it a tragedy? No. Is our language becoming degenerate? Of course not. That preposition thing is just about thinking some other language with dative case markings is better than ours. Feh, I say, to that.
And don't get me wrong - I have no problem with people who prefer to say "To whom did you give the book?" I just want to rip throats when some supercilious little twit berates someone else who says the perfectly acceptable "Who did you give the book to?"
This is the problem of being a linguistics geek. I don't care about prescriptive linguistics. I don't care what someone 50 years ago says is the correct way to insert "that" into a complement phrase. Languages are supposed to change, damnit. If they didn't, we'd still be speaking Old English (at the very least) - possibly Nostratic or some other such thing.
I think what really set me off was happening across some entry about "Well, my high school English teacher said...[insert stupid frozen rule here that poo-poos a perfectly sensible way of using language for emphasis]". And don't get me started on the Standard Written Test of English that's made its way back into the SATs. Grrr.
[geek geek geek]