here are my two cents on the subject.
I'm plagued with a marked attention deficit :P, so when I found out about WriteRoom I was sold on the idea of full-screen distractionless editing.
now, I'm not too fond of feature requests, but I'd like allan to take a look at WriteRoom and think about offering similar functionality within TextMate (snippets + fullscreen = wow!) — megazoomer just doesn't cut it, the whole text is jammed over the left border, too ugly to be true!
on the other hand, since I first used a mac I expect the maximization button to act like it does in Finder, i.e. increase window height until the whole content is shown. that was the behaviour I got on BeOS too (I was an eager BeOS user back in the day). I guess offering those two modes (full screen and vertical window zooming) would be very nice.
ciao,
domenico