So I recently noticed that most of the email questions I get are about RTF! I think of RTF as The Battered Little Document Format That Could, and sure I do find it handy to generate RTF -- but I never expected it to be quite so popular. Relatively speaking.
My surprised but gradual realization that there was no book on RTF, made me go write one. And now my surprised but gradual realization that there's no email list or newsgroup for discussing RTF has led me to make RTF-L. And it's barely a day old, and people are already sanely discussing things on it.
My next "plan ten hours to write one hour of code" project will probably be RTFFO, an XML lect meant for turning into RTF.