I like "WriteRoom!" I just downloaded, installed and launched it. The first 'test' for me, was to see how quickly and easily I could get it from the initial 'Full' screen mode back to where I have access to my other notebook controls, applications and what not - a simple press of the escape, "esc," key did the trick :)! It also incorporates 'as you type spell checking' - sweet :)! The fact that it's "free" doesn't hurt either :)!
As far as the "need to paste the text into a different app to output (e-mail, word processor, text editor, whatever" goes, I routinely use 'text editors' to compose messages for various reasons - message boards, email, etc., then "copy and paste" to get the completed message where I need to in order to post or send it. So this is not an issue with me.
I did notice when trying to underline a single word, it underlined 'everything,' ditto when I tried to italicize a single word :). So, it still needs a 'little' work, but I plan on making use of it as is right now! By the way, I used "WriteRoom 1.0 beta (5) to compose this comment. I hope my couple of cents proves useful to someone out there. Oh, if you prefer colors other than the default green on black - which takes me down memory lane and my "MS/PC DOS" days :), you can change it in the preferences.