The Nook is styling my fragment identifiers <a id= > in the same way as I've styled a:link and a:visited. I'm at a loss as to how to override that. Can anyone help?

Pseudo classes (:link and :visited) are not always correctly supported, the Nook is probably applying the same style to all <a>.

But you don't have to use an <a> to have an identifier (an anchor to link to), you can add the "id" to any other element:

<p id="target">Any link with href="#target" will point to this paragraph.</p>

Jellby, I love you. Thank you SO much. Right now, I'm also fighting to remove the three letter indenting Nook is so "generously" applying to all my <p> formatting.

Marcia,
I would suggest just using nice clean styling and not trying to fight the nook options (especially the user selected styling options). If the user prefers to have your styling, then they can select "Publisher Defaults" to be On in the text dialog. Anything other than that will be an exercise in frustration for you - as what will happen will change from dot release to dot release.