LOL! Honestly, being a grammar and spelling Nazi that I am, I try as much as I can to avoid it. It doesn't really bother that much when I read it...but if its really messed up like writing "mi" instead of my and mixing up their, they're and there....it seriously pisses me off
Sometimes when in makes absolutely no difference in the length of the word it's annoying... like writing "tyme" I'm like huh? Seriously what difference did that even
make?
and just to prove the Grammar Nazi-ness of me... (don't hate me, plz) it's "come up with
they're their own spelling"
Gosh..I know how annoying I must be right now
But will it really affect our day to day writing? In my opinion yes, because I've seen in first hand and sometimes without noticing it you write u, r and things like that. But it really depends if it's in a chat log/ forum or text message, since for a text message its much cheaper and quicker to type short things.
Overall, its convenient...but not advised. Sometimes it is necessary (such as passing notes in class xD and texting your friends, or when you have no time) but it's not "healthy" to use it
ALL the time.