Now, for a contrarian view (hey, that's one thing I'm good at): I think I'd get little argument from linguists when I point out that English orthography (the system of writing and spelling and its correspondance to speech) is far from logical. I mean, you've all seen the example of the "correct" way to spell "fish", right? For those who haven't:
ghoti = fish. "Gh", as is lauGHter, "o" as in wOmen, "ti" as in attenTIon.
More than many other languages, English spelling requires the ability to remember a lot of purely arbitrary rules, exceptions to the rules, and exceptions to the exceptions. There is even considerable evidence that spelling and reading are partly a function of recognizing the correct overall "shape" of the word on the printed or written page, and other pattern recognition abilities. Those abilities are not necessarily correlated to overall intelligence or even education, any more than the ability to (say) mentally manipulate 3-D shapes in one's mind, or to easily comprehend higher mathematics. I have good language abilities (and some others) but am a mathematical (and otherwise) idiot. Some brilliant scientists can't spell worth a rip. There are lots of dimensions to "intelligence" and education, and very few are good at all.
The emphasis on spelling and grammar as markers of intelligence are purely social constructs; prejudices, if you will.
For that matter, any editor will tell you that the manuscripts of even professional writers are often rife with spelling and grammatical errors.
Historically speaking, the whole concept of standardized, "correct" spelling (by the way, the UK and much of the English speaking world consider "standardised" the correct spelling) is quite recent - only since the widespread compliling and publishing of dictionaries in the 19th century. Before that, spelling was pretty much "made up", even by the most educated people as you can easily see by reading unedited quotes from letters, literature and such from the past.
And of course, the immediacy of posting on a forum like this militates against things like proofreading, editing. This is not like writing a book or term paper, after all.
But anyway; y'know my pet peeve? Misplaced apostrophes. Bug's the heck out of me!
So THEIR!