It's a speed and economy issue: in a chatroom or on a messenger, it helps to have some shorthand otherwise conversations become very, very slow. Using caps-lock slows you down too! In one sms, you have a limit to the number of characters you can type, so once again some shorthand is really helpful. However, I can't count it as "normal" because outside of sms or chat (ie. in an email, letter or even in an online comment) it looks illiterate and childish. Yet I can't complain... it's nice to know who can tell when it is appropriate, and who can't. ;)

I would say A and B. It helps save time and energy to type such abbreviations, and since it began, more and more people do it, thus it has become a convention. It is acceptable for quick phone texting, and often on the internet, but I would not recommend it for more professional/business communications.

C. It's laziness. The only exceptions are in SMS and IM chat, when it is acceptable. In any other situation though, it is not appropriate.

I think this is normal thing , frist it's simple . second just like you answer it's a habit.

I tried to use correct method to witten when I was chatting. I found It is very very difficult to use caps-lock especially my English is not good enough. So I agree with A. But I also agree with Richard, Peachey and James. You let me know when abbreviate is allowed and when it is not appropriate.