Well, Ive used http://www.junitdoclet.org/ (why doesnt the URL tag work???) once, but stopped using it because I found that my unit tests selfdom have a one to one match with how a class looks like. Sometimes they do, but mostly they dont. I also dislike all the comments JUnitDoclet puts in my code, but thats personal taste.
There seems to be an upcoming release 2.0 for JUnitDoclet, but I havent checked the activity in CVS if this is soon to be arrived.