Is there a way to do drag-and-drop re-ordering of the preview elements in a dropzone.js instance?

I've got it working now using jquery-ui's sortable. The trick was to make sure to use the 'items' option in sortable to pick only the dz-preview elements, because dropzone.js has the dz-message element along with the dz-preview elements in the main container. Here's how my code looks:

The HTML:

<div id="image-dropzone" class="dropzone square">

The script:

$(function() {
    $("#image-dropzone").sortable({
        items:'.dz-preview',
        cursor: 'move',
        opacity: 0.5,
        containment: '#image-dropzone',
        distance: 20,
        tolerance: 'pointer'
    });
})

Besides the code from ralbatross you will need to set the order of the file queue of dropzone..

Something like:

$("#uploadzone").sortable({
    items: '.dz-preview',
    cursor: 'move',
    opacity: 0.5,
    containment: '#uploadzone',
    distance: 20,
    tolerance: 'pointer',
    stop: function () {

        var queue = uploadzone.files;
        $('#uploadzone .dz-preview .dz-filename [data-dz-name]').each(function (count, el) {           
            var name = el.getAttribute('data-name');
            queue.forEach(function(file) {
               if (file.name === name) {
                    newQueue.push(file);
               }
            });
        });

        uploadzone.files = newQueue;

    }
});

And remember that the file is processed async, i keep an hashtable for reference when the file is done and save the order at the end.

It doesn't work with duplicate filenames

Here's another option without any plugins. On the success event callback, you can do some manual sorting:

   var rows = $('#dropzoneForm').children('.dz-image-preview').get();

    rows.sort(function (row1, row2) {
        var Row1 = $(row1).children('.preview').find('img').attr('alt');   
        var Row2 = $(row2).children('.preview').find('img').attr('alt');
        if (Row1 < Row2) {
            return -1;
        }

        if (Row1 > Row2) {
            return 1;
        }
        return 0;
    });


    $.each(rows, function (index, row) {
        $('#dropzoneForm').append(row);
    });