Should book titles be contained in an <em> tag? If not <em> is there more appropriate markup?
<em> is definitely wrong. In addition to the other suggestions given before me such as RDFa or a semantic class name, consider using <cite>
From the HTML 5 draft:
The cite element represents the title of a work (e.g. a book, a paper, an essay, a poem, a score, a song, a script, a film, a TV show, a game, a sculpture, a painting, a theatre production, a play, an opera, a musical, an exhibition, etc). This can be a work that is being quoted or referenced in detail (i.e. a citation), or it can just be a work that is mentioned in passing.