I know of two tag libraries that are in dire need of unit tests - the displaytag and struts-menu. Both have no tests. I've looked briefly at TagUnit, but aren't you just writing JSPs (with custom tags) to test JSPs? I'd rather have an Ant/JUnit driven solution. Also, are there HTML versions of the user guides for TagUnit (Simon ;-)? I hate PDFs.
So my question is - how do you test your tag libraries?