I'll tackle the meditative part first. For a long while I thought that desktop web applications were utterly pointless, because a) the GUI is there anyway, and b) embedded HTTP daemons cost so much in overhead (for example, I started playing with embedded Tomcat recently; cool concept but enormous RAM hog and a 10MB installation (which is a lot if you're offering something for download)). Then I saw the Google Desktop Search and that changed my opinion. So now my answer is "if it's the sort of thing that would make sense in a normal web app, it makes sense as a desktop web app."
<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>