On the internet, with few exceptions,
words,
text, are how we see one another. There is no other way (short of
hi-jacking the Internet2 for your personal video transfer needs) to reliably come in contact with people.
All the popular modes of internet communication are primarily text-based: the web, IRC, ICQ, e-mail, MUDS, forums, news, and Quake (as well as all other online games, barring a very few with voice chat). If you're online, you're going to use words. There are no if's, and's, or but's.
So... since this is the only way most of us are going to perceive you, why not take the time to learn how to use them?
Work on your typing. No one likes reading text that's lal mesdsed pu becuz u'r 2 layz to typ t. At least _try_ to use punctuation. Even if it isn't 100% right, it helps tremendously to have periods, for instance. Commas' are good, too.
Work on your grammar. Some of us like to follow the conventions set forth in the English Language to speak. It certainly makes it easier if you at least _try_ to be grammatical. Even if it will easy to read, which it sometimes are, bad grammar's just another reason for people to ignore you.
Capitalize properly. Capitalizing Things that are Important was in Style... in the mid 1800's. Consider going for modern grammar.
And why should I try to type well, anyway?
Because the way you type is the only way we have to perceive you. If you type poorly, we, by association, come to see you poorly, at least at first sight. If you type well, then we, by association, come to see you as being competent. It's the difference between showing up at a party wearing a dirty bathrobe you haven't washed in a month, and showing up in nice, clean (although not necessarily fancy) clothing.
Our opinion of you as a person can be independent of your appearance, but when we first meet you, it often isn't. First impressions count for something.
What about style?
Style is great. I often break the rules outlined above for effect, to carry meaning. Like referring to something as a "Good Thing" instead of a "good thing" - it makes people pause, carries meaning. But I do know how to follow the rules - that is why, when I break them, people know that it is intentional, and not my own incompetence at work... I over-use ellipses, for one thing :), and I like to mis-use (over generalize) grammar from time to time, but if you stick me in front of an english language competency test, I'll ace it.
You have to know the rules before you can break them.
(Evidence: I got a perfect score on my english section on the SAT II. Just so y'all can't dispute me...)