Kottke writes about a 56-year-old prediction of a positive effect from television on literacy, and notes that predictions for “television” closely resemble the modern web.
A lot of modern communication technology is textual which, a few decades ago, when television and home video were at their height, would have seemed odd. But it turns out that text is more efficient than audio and video. I think this is because basic literacy levels have improved: people are generally expected to be able to read and write text, which has made text-based technology convenient, and has also improved the rate of basic literacy.
This means that lots of people can use text to communicate; it most certainly doesn't mean that those people are using good-quality written language. Ppl r in ur intArnet, revelin in intenshunly wierd gramr. It's reminiscent of an intentional misspelling fad in nineteenth-century America, from which the word/phrase “OK” is suggested to have arisen.
Where, when I was a lad, kids would only use text when writing for their teachers, who would then correct and frown upon misspellings and poor grammar, now children talk amongst themselves using text—internet instant messaging, mobile phone–style text messages and emo blogs being the primary culprits. (Be nice to LiveJournal—it's felling lonley rite now.)
So people get used to using unconventional or incorrect (depending on your viewpoint) spelling and grammar, with the understanding that the receiving party will nonetheless be able to understand the message. (This is compounded by a general reluctance to correct or be corrected.)
Where this compresses communication, for example by abbrev.—making it quicker and generally more efficient—this is not a bad thing. There are a set of essentially universally–recognised abbrev's, e.g. “e.g.”, “&”, & “etc.” etc.; numeral figures and mathematical symbols can also be considered examples. A problem only arises when meaning is misinterpreted.
Some help for English-learners and by way of an example: more often than one might expect, “then” actually means “than”. “More often then one might expect” doesn't actually make any sense and “then” sounds similar to “than”, so most experienced English-speakers can understand the message. “There”, “their” & “they're”, and “to”, “too” & “two” are two other classic examples of words being conflated.
My point is that whereas before the advent of recent technology a smaller number of people had a greater quality of literacy, now a greater number of people has a lesser quality of literacy. It's as if the ubiquity and the quality of literacy sum to a constant.