You always have to write the letter "I" large. "Yes, I did that." Not, "Yes, i did that."
What I see mostly within the game is the "gamer speak", for example, "Hi y r u here?" This is fine on Forums (I guess) but in game, such things should never be written like that. Instead, just write "Hey, why are you here?" It's easy if you get used to it. ^-^