gistfile1.js

// Initialize
$('#progressbar').progressbar({ value: 0 });

// Record current position in a list
current_position = 0;

// Record list length
list_length = $('li').length;

// Loop through the list
$('li').each(function() {

     ... do something ...

     // update progress bar
     $("#progressbar").progressbar("option", "value", current_position/list_length * 100);
});