Food for thought in this article in the Guardian by Thomas Jones, the editor of the London Review of Books blog.
Jones hangs the article on the Bad Grammar award given by Toby Young and two other judges to the letter sent to Michael Gove by 100 "bad academics". Toby Young claims that the letter is so bad that it makes the case for rigid teaching of grammatical 'rules'. Jones reckons the award has more to do with politics than grammar.
Jones quotes from Steven Pinker's book The Language Instinct.
"Since prescriptive rules are so psychologically unnatural that only those with access to the right schooling can abide by them, they serve as shibboleths, differentiating the elite from the rabble."
He goes on to examine several "rules" - some of which are mere conventions, some of which are in the process of changing, and some of which are worth following because they lead to more elegant, clearer writing.
I shall remember Pinker's quote - or the gist of it. Spot on, I think.
Another article worth reading, by David Crystal