Deliberately typing incorrectly is a bit annoying, but can be a great help to those who are unfamiliar with a keyboard. If you're capable of typing three or four words a second then there's no need to shorten or alter words. However, if you're a slow typer then using OMGWTF-speak makes things a lot quicker.

Nevertheless, I don't like that style of writing at all, and I'd prefer it if no-one used it at all. I'm prepared to forgive a few spelling mistakes/typos if it makes the post easier to read, and as others have said, using proper English makes you seem more mature, and makes your fellow members pay more attention to you.