I think it heavily depends on the kind of content you are consuming. I know it is anecdata, but my personal grammar and spelling skills went all the way up since I started using internet heavily (which was very noticeable to me, since english isn't my native language). And while I use a lot of incorrect grammar and spelling when talking to friends, I usually do it out of convenience (to shorten words, etc.), not because I don't know the proper grammar/spelling.
English isn't my first language. Yet, I believe my english grammar is getting worse even if I read a lot of English everyday. I blame this on globish though and the fact that it's relatively rare to get corrected on grammar mistakes around here.
