The start of a 'dirty' input tracking plugin. It's been done a bajillion times, but this one is simple.

dirty_form.js

/* -------------------------------------------------------------------------- */
/* DIRTY FORM
/* Checks to see if the user has made any changes to a form. Toggles the save
/* control on or off appropriately. Also prompts user to save it they attempt
/* to navigate away with unsaved changes.
/* -------------------------------------------------------------------------- */
(function($) {
  var DirtyForm = function(form) {
    this.$form = form;
    this.$save = form.find('button.save');

    var inputs = form.find(':input:not([type=hidden], button)');

    this.originalValues = _.reduce(inputs, function(memo, el) {
      var $el = $(el);
      if (!$el.is(':radio, :checkbox') || $el.is(':checked')) {
        memo[$el.attr('name')] = {
          value: $.trim($el.val()),
          dirty: false
        };
      }
      return memo;
    }, {});

    this.setPristine();
    inputs.on('change', $.proxy(this, 'change'));
    $(window).on('beforeunload', $.proxy(this, 'navigate'));
  };

  DirtyForm.prototype = {
    change: function(e) {
      var $input = $(e.target)
          original = this.originalValues[$input.attr('name')],
          val = $.trim($input.val());

      original.dirty = (original.value !== val);
      var dirty = _.some(_.pluck(this.originalValues, 'dirty'));

      if (dirty) {
        this.setDirty();
      }
      else {
        this.setPristine();
      }
    },

    setDirty: function() {
      this.dirty = true;
      this.$save.prop('disabled', false).css('opacity', 1);
    },

    setPristine: function() {
      this.dirty = false;
      this.$save.prop('disabled', true).css('opacity', 0.5);
    },

    navigate: function() {
      if (this.dirty) {
        if (window.confirm("DERP")) {

        }
        else {
          // supress event
        }
      } 
    }
  };

  $.fn.islayDirtyForm = function() {
    this.each(function() {
      var $this = $(this);
      if (!$this.data('islayDirtyForm')) {
        $this.data('islayDirtyForm', new DirtyForm($this));
      }
    });
    return this;
  };
})(jQuery);

simpler.js

(function($) {
  function DirtyForm($el, opts) {
    this.$el = $el;
    this._dirty = false;
    this._originalValues = {};

    this.settings = $.extend({
      // Add default settings here.
    }, opts);

    // Subscribe to any event on the form
    var inputs = form.find(':input:not([type=hidden], button)');
    for (var i = 0; i < inputs.length; i++) {
      var $el = $(inputs[i]);
      if (!$el.is(':radio, :checkbox') || $el.is(':checked')) {
        this._originalValues[$el.attr('name')] = {value: $.trim($el.val()), dirty: false};
      }
    };

    inputs.on('change', $.proxy(this, '_change'));
    if (this.settings.preventNavigation) {
      $(window).on('beforeunload', $.proxy(this, '_navigate'));
    }
  }
 
  DirtyForm.prototype = {
    isDirty: function() {
      return this._dirty;
    },

    _change: function() {
      var $input = $(e.target)
          original = this._originalValues[$input.attr('name')],
          val = $.trim($input.val());
 
      original.dirty = (original.value !== val);
      var dirty = _.some(_.pluck(this.originalValues, 'dirty'));
      if (dirty) {
        this._dirty = true;
        this.$el.trigger('dirty', true);
      }
      else {
        this._dirty = false;
        this.$el.trigger('dirty', false);
      }
    },

    _navigate: function() {

    },

    _run: function(name, args) {
      if (typeof this[name] === "function") {
        return this[name].apply(this, args);
      }
      else {
        throw "$.fn.dirtyForm does not have a function called " + name;
      }
    }
  };
 
  $.fn.dirtyForm = function() {
    var args = Array.prototype.slice.call(arguments); 
 
    for (var i = 0; i < this.length; i++) {
      var $this = $(this[i]);
 
      if (!$this.is('form')) {
        throw "$.fn.dirtyForm can only be called on form elements";
      }
 
      if ($this.data('dirtyForm')) {
        return $this.data('dirtyForm')._run(args.shift(), args);
      }
      else {
        $this.data('dirtyForm', new DirtyForm($this, args[0]));
      }
    });
 
    return this;
  };
})(jQuery);