I think, if anything, the internet is making people more articulate. I'm in several online communities that aren't devoted to writing (AW is hardly a fair test of, lol), and most of the young people who've grown up with the internet are shockingly articulate in writing, even more so than I was at that age. It's because so much of the internet is text-based, and these kids spend ALL their free time online. They're reading and writing ten times more than people did pre-internet. In fact, the worst posts on my other forums generally come from older people who grew up pre-internet. They've obviously forgotten everything they ever learned in school about grammar and spelling, probably from lack of use.
It might be worth noting that a lot of places, including the other online communities I participate in, have banned chat-speak because serious writers aren't the only ones who find it annoying as hell.