You may have lately noticed the ever-increasing prevalance of leetspeak as you surf the highways and by-ways of the infobahn. (It's also known as 1337, and is a short form of "elite"). The difference between this new jargon and the standard English they used to teach in school is more than just a few numbers or a few oddly-spelled words; it's a difference in the way we define what language is, how it grows, and how we -- as users -- grow with it. It's why you may start seeing the word "teh" a lot more.
But first, let's address the origins of leet. One probable explanation of its origin is from bulletin board systems 80s. It started with people trying to talk about illegal or otherwise questionable activities, such as software piracy, that some BBS operators did not want to be discussed or carried out via their systems. The operators would filter out certain words or ban people who used them. Most notably the word "hacker" was a common banned word. To get around this ban, some users would substitute characters; for example, "hacker" could be replaced by "hack0r," "h4cker" or even "h4x0r." This phenomenon has now grown to encompass a variety of language alternatives. (Thanks, Wikipedia!)
So what happened to "teh"? Hang on a sec.
Your dictionary is prescriptive -- it teaches you the correct way to spell words, the correct way to pronounce them, and the correct way to use them. Leet, on the other hand is more descriptive; it is not a guide to writing in the 21st century, but rather a snapshot of how we are already communicating.
Our age is one of finger-driven communcations, usually quick and usually error-prone. Whether it's due to those tiny keys on your Trio, or a failure of the word-guessing software in your cameraphone, or just some geeks screwing with each other, there are a variety of new, common, and accepted mots d'argot that have crept into our written communications. I take as my primary example the word "teh."
You've seen it, I'm sure; it's a common typo for "the" and, when you're sending a quick message to a buddy from a concert or your local java shop, it's more than likely you've sent this mangled spelling instead of the proper Queen's English. But leet doesn't correct you -- leet embraces this. With millions of people typing "teh" instead of "the," the former is now considered, among the technorati elite, as an acceptable alternative.
Purists will chafe at this last statement. For what use are the rules of grammar or correct spelling if they can be so easily usurped? Thank heavens, they proclaim, that Webster has not yet tread down this primrose path.
And I have, at times, been accused of being a member of this crowd. An English major in college, and still one to the core, I'm the guy who criticizes your use of "torturous" instead of "tortuous" and loudly wonders why you can't learn to use adverbs. And finds this funny.
But I'm liking this "teh" hubbub, bub. Why should we be trapped within the confines of a dictionary that can no longer keep up with the rapid pace of language change? Why should we deny ourselves the more meaningful ways of expression that seem so apropos to our new methods of communication? Sure, we all got real tired of emoticons real quickly, but they're dying the death they deserve -- spoken language takes care of itself.
"Teh" and "evar" and "n00b" (and the rest) will survive only if they have value. Don't worry that you'll find yourself unable to understand the tax return forms next year -- I assure you, they won't be quick to change. But the slang that proves useful will stick with us, and will one day be found in the hallowed, yellowing pages of your tree-based dictionary.
You won't find me typing "teh" anytime soon (except in the case of typographical errors), but I hereby declare my approval -- screw with my mother tongue, please; just keep it alive and relevant, and I'll do my best to keep up.