Since I don't have Opera on any of my machines, I didn't test it on that (at the end of the write up that the link points to, I note that I only tested it on a limited set of browsers).
The fellow that created the CSS Pencils test also noted to me that it doesn't work in Opera. It is some bug in the way I did the CSS, but it doesn't mean that it won't work at all - just takes some tweaking.
But yes, if your browser won't render the DIVs correctly, then you sure aren't going to see much of anything useful.
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>