Seriously, I'm sick of everyone who uses hard-to-read chatspeak using the "We're not in school!" excuse. And I'm not exaggerating, basically EVERYONE uses that excuse to justify typing like a total retard.
From what I've experienced and what I've seen, it's school that MAKES people type like that. In school you're FORCED to me this, FORCED to do that, when you finally get out of school? It's the first proper taste of freedom for a lot of children/teenagers. So they just go wild.
Personally I was, and still am, homeschooled. Therefore I have had to freedom to write as I please, so I tend to use proper grammar when emailing/chatting to people online. Although when I'm talking to my best friends, sometimes we use horrible grammar for the fun of it, kind of in a humorous way.