I am beginning to fall in love with jQuery. Screw you, bicycle inventors! :-)

    function next_step() {
        // note how elegant and self-explanatory this code is.
        var cl = 'step_selected';
        $('.' + cl).removeClass(cl).next().addClass(cl);
 
        // Also look at previous version of the code,
        // before I remembered about chaining methods.
 
        // var li = $('.step_selected');
        // li.removeClass('step_selected');
        // li.next().addClass('step_selected');
 
        // Not as sexy, right? :-)
    }