While I'm a strong supported of the necessity for people to avoid the "SMS talk" (cmon,ppl! m prity sure u no wat I mean) in writing on a different media (in which you don't pay for each character you're using), I do believe though that acronyms are not to be despised like this.
Without going deeper into the analysys of languages and their tendence towards a progressively simplification, both in speaking and in writing, I think acronyms are still to be considered something that enriches the language; they allow for economy of understanding and expression, and condensation of meaning and semantics.
Of course, you could write "As Far As I Know" but do you see how more powerful is AFAIK as an espression? it's short, direct to the point, and conveys the same meaning. Reading online on a PC or mobile screen doens't give you the luxury of using a lot of words, engaging in complex and long sentences, like those 19th century writers payed by the word. You need to be concise and fast, or you'll lose readers' attention (much like this post is doing), and acronyms (especially in a language like english that tends to contractions, think at "I'm", "won't", etc.) are just the right things for the job.
As long as you make yourself clear, by using standard and well-know (and recognized by the community) acronyms, I see nothing wrong in this. I'm not talking of course of the "techincal acronyms", but the one used in common language and in lieau of idiomatic expressions (sorry I don't know the right english term for this, something like "expression figée").
And, besides, you cannot compel someone to always write in its purest and formal language, for many of us have learnt enligsh as a second or third language, and with the internet and its ever-growing use of acronyms as a teacher.