I will forgive people for using it if they are actually texting me on a phone.
In that case I am aware that it is much easier and quicker to type in text speak.
It takes me a very long time to text things because I insist on typing in full.
However, what really annoys me is when my friends will send messages to me via Facebook or other Instant Messengers while on a computer and will use text speech.
They have absolutely no reason to do so. They are in no rush and have no need to type quickly.
I will let people off for avoiding correct punctuation, although it annoys me, but if you are sat at your computer and you decide to shorten every word to 4 characters or less then I don't care to speak to you.
If it takes me the same time to type something in full as it does for you to type in text speak then there is no excuse for you to not type fully as well.
I personally will shorten words down to some text speech, but only in the scenario that I am talking to a friend in a relaxed manner. And in that case, I'm not going to use it every sentence or constantly.
I'll use words like "lol" and "cya" but little more. 99% of my words will be written in full.