Okay, you want the NewClassic approach to "Internet Literacy" do you? Oh my... Where's my red pen?
Capitalization
Those who argue capitalization is unimportant must write the sentence "I need to go help my uncle Jack off a horse." 500 times on the board. Honestly, this is just as important as anything else. If for no other reason, the difference between i and I could help me identify typos (it magically turns into i more often than most realize), helps me read the sentence, and directs the flow of the sentence in a more reasonable manner. Anyone who doesn't do so, in IMs or otherwise, is essentially lowering my reading speed and making me doubt their self-worth. If they can't take themselves seriously, then why should I, regardless of the topic in question. (I'm an English major, so excuse my obsessive attention to grammatical detail.)
Spelling
Typos, errors on difficult words or homonyms, and the occasional slip-up is fine. What isn't fine is deliberate use of unnecessary shorthand. Seriously, if you use "b8" instead of "bait," to increase 'efficiency,' then you're lying to yourself and me. If you look at your anyone that's a practiced typist (short of accountants), then you can hit "ait" faster than you can usually hit "8" because of the way you process the letters of the keyboard versus the number line. Not to mention you're short-handing a four letter word. Seriously guys?
Professionalism
Mourn its loss, folks. I just saw someone use "thru" on a formal, 5-page essay, and did not get a negative mark. "Thru" has become acceptable shorthand in formal writing. Does this bother anyone else? If not, then perhaps I'm the only one that's scru'd.
Culture Shock
As far as British (or Australian, or Canadian, okay, everywhere but America) versus American spellings don't bother me as much in context. Granted, if I write a lot of intelligent things, and you get hung up on the fact that I used "aluminum" or "color" but ignore the rest of the discussion, then stop reading what I have to say. If you grew up learning to spell "mnemonic" as "numonic," then I wouldn't get on your case. It's how you learned, so why give me hell for the fact that I perhaps learned it a different way. It's not wrong to have an ulterior established convention, it's simply different. No more, no less.
And, that's all I have to say. The only English rule that I don't personally observe are the more highly advanced ones, like ending in prepositions. Honestly, "That's something I won't put up with." is a fine sentence, phrasing it correctly (That is something up with which I will not put.) is convoluted and unnecessary, and doesn't detract from the statement. Does that make me odd?