staff:

We’re about to start rolling out a bunch of features focused on interaction between tumblelog authors and their readers.  Post notes are going to be the glue for all of this interaction, so we’d like to ask all theme designers (and anyone with custom themes) to incorporate this new tag:

{PostNotes}

This will render the post’s notes (including reblogs and likes) on their permalink pages.  Check out an example on my tumblelog.

Unlike our other theme tags, this outputs generic HTML markup, so all you need to do is style it with CSS.  Here’s a basic stylesheet to get you started:

ol.notes {
    padding: 0px;
    margin: 25px 0px;
    list-style-type: none;
    border-bottom: solid 1px #ccc;
}

ol.notes li.note {
    border-top: solid 1px #ccc;
    padding: 10px;
}

ol.notes li.note img.avatar {
    vertical-align: -4px;
    margin-right: 10px;
    width: 16px;
    height: 16px;
}

ol.notes li.note span.action {
    font-weight: bold;
}

ol.notes li.note .answer_content {
    font-weight: normal;
}

ol.notes li.note blockquote {
    border-color: #eee;
    padding: 4px 10px;
    margin: 10px 0px 0px 25px;
}

ol.notes li.note blockquote a {
    text-decoration: none;
}

You can get the full documentation (including complementary tags like {NoteCount}) on the Custom Themes page.