Pretty much never. If I'm in a rush I will text without any punctuation, attention to capitalization, and possibly more abbreviations (common ones, but I never use them), but that is as far as I will go. Sometimes I won't care much about typos, in this type of situation.

Some days I do get lazy (even when on the computer) with my punctuation and wording.

And like Corey, I also do it when I'm trying to be sarcastic and/or or goofy.