I think I remember reading a post by someone that claimed if you received a text while browsing in landscape mode, you could respond to the text in landscape mode.
I can't recall the details or possibly know if the claim has any validity, but I would be curious to know if anyone can verify or disprove this?
Either way it is something that is easily implemented in an update, and due to the massive demand I have seen for landscape texting around forums and news sites I am hoping that Apple has taken notice as well.