When you write a new message you have an option to select the screen size which is a great idea. What would be even better is if that also increased the length of the edit box, not just the width. Currently writing long message is a bit of a pain, especially if you've quoted someone.
Keep up the good work!
The width is changed via javascript, but I'm not sure if you can change the number of rows of textbox forms via javascript as well? I will have to look it up, but I don't think you can...