I started working on this for fun and made a lot of progress over my winter break time: https://github.com/snoopdave/rollarcus/tree/bootstrap-ui. I'm rewriting all JSP pages to use Bootstrap and using the Struts-Bootstrap plugin where it makes sense.
I've finished the main menu page, entry editor, entries list and categories pages so far. I hope to complete the rest of the pages over the next couple of months. If anybody wants to help with this, I can merge the code into the Roller SVN repo in it's own branch (though I do prefer Git). Dave