Countless times I find myself forgetting details about somebody elses post I am replying too and I have to copy what i've already typed, go back and reread their post, and then come back and paste what I have and keep going. It's a big hassle and I'm sick of it! I think that on the reply box screen it should show the thread you are replying to that way if you are trying to answer a bunch of questions you can just type out answers as you read the thread.
Another suggestion, which I know has already been stated, is to make the message reply box a whole hella lot bigger. It's too damn small! I'm always having to scroll up and down to reread everything instead of being able to just look at it and know what's going on.