Hi Grant, and welcome to Using English.
I used to think that the Internet was having a bad effect. But then I started really paying attention to my own child, a teenager. Her writing in e-mails to her friends makes my cringe: Hy! Meh... All kinds of non-words and random punctuation.
Then I read her essays that she writes for school. They are perfect.
I don't think that ghastly Internet speech has improved anything, but it hasn't distracted from her abilty to write good, cogent arguments using entirely standard English.