Select values of checkbox group with jQuery

You could use the checked selector to grab only the selected ones (negating the need to know the count or to iterate over them all yourself):

$("input[name="user_group[]"]:checked")

With those checked items, you can either create a collection of those values or do something to the collection:

var values = new Array();
$.each($("input[name="user_group[]"]:checked"), function() {
  values.push($(this).val());
  // or you can do something to the actual checked checkboxes by working directly with  'this'
  // something like $(this).hide() (only something useful, probably) :P
});