At the moment to write this post I am both scrolling back and forward and seeing my screen scroll just to see the whole text box. So to read properly I either have to zoom out and look at size 3 font or try to scroll back and forth with the feel of reading a newspaper through a magnifying glass. If you don't have scrolling you could reduce the font a touch, take out sigs, and just limit headers to names and an avatar.

You'd also may want to think about a static dropdown menu at the top to allow for easy navigation. With some of the really long threads it would become a pain to scroll up to the top by swiping the screen 50 times.