You save like 0.1 seconds writing “u” instead of “you” at the cost of making yourself look like an absolute idiot. Is there any reason you’re trying to shave off this time? Are there wild dogs bearing down on you as you write why we need another look at Obama’s birth certificate? If so, run from the wild dogs and write your comment later. Your whole sentence shouldn’t scream, “I’m a useless idiot with nothing important to say.” You should never write like that unless you actually are a cat expressing your desire for a cheeseburger.
Frank J. Fleming, Tips for Not Appearing Crazy on the Internet.