LOL, Gunnie ;D That link is funny. But to me personally, this type of language is more difficult to read as well as to write. I would have read the posts in the link you provided 10 times faster if they were written in plain English. Maybe it's "cool" or whatever ... for young people, but I don't see any appeal in it. In my opinion it distorts the English language and is just very distracting while reading. This kind of thing is definitely not for me. It would take me 10 times longer to write something in "I337" than in plain English. I'd be wasting my time.
Most people think that young people all understand the different ways of comunicating, like I337. I'm 14, and that took me ages to read and understand. It's way to complicated for me. ;D I only sometimes use a '2' instaed of 'to', or '4' instead of 'for'. Not many people around me use it.
1337 is almost never used outside of the communities of online games. It's mostly used as a joke and for names - in some games, because names have already been taken, for example, they'll use the name in 1337 which is essentially the same thing. So Marc could be M4rc or any of the different varieties.
Chatspeak (whatever you want to call it) is VERY different - it's just shortcuts for words. Like u meaning you, and 2 for two/to/too. 1337 is more of a code/joke/etc.