I personally can't stand "txt speak." I also never use it even when sending messages from my phone.

However, I think it can be acceptable from a phone because you might not have the extra time for whatever reasons, and it can be difficult if you don't have one with a full keyboard. (I have to add that I got a new phone with one recently and I don't know how I lived without it. )

But if someone has the time to sit here and read threads with sometimes dozens of pages, I think they have the time to type out full words..