I have a good number of friends with only a bare minimum grasp of English, so for the purposes of casual conversation, I find myself extremely lenient. Do I prefer proper spelling, grammar, and capitalization? Of course. But I don't find it necessary as long as it is legible and coherent. Plus, I make my own share of absolutely bewildering typos, so it's not like I am in a position to judge people.
If I were reading a book or in a more academic setting, however, I would expect a certain degree of professionalism. I'm not going to get mad, for instance, about ending a sentence with a preposition or some other obscure English rule that nobody follows in real life. But I remember having instructors in college who would type like they text or be otherwise completely illegible. And the advent of the eBook has certainly helped progress the creative endeavors of writers who are apparently allergic to the editing process, though it's not as though traditional publications are completely exempt from this, either.
On the other hand, I find people who correct things like your/you're to be completely insufferable. You clearly understood what I meant. And don't pretend like you don't make the same mistake. So get off you're high horse and respond to what I said, or your going to be in for a world of hurt!