I usually export RTF using XSLT, but it's not user-friendly at all. Neither XSLT nor RTF win any beauty contest in hearts of most developers :)
Sometimes people do the following: they create HTML with all the formatting, save it (e.g. by exporting a single global field) and then open it in Word or Excel. The latter can import HTML pretty well, so you can get a Word or Excel document with some formatting.