Dead simple function to serialize a form as a JSON object, using '.' notation in the field 'name' attribute and only serializing fields with a class of 'serialize'.

serialize-form-json.js

    window.serializeFormJSON = function(f) {
        var json = {},
            $f = f.jquery ? f : $(f);
        
        $('input.serialize, select.serialize, textarea.serialize', $f).each(function(index, node) {
            var keypath = $(this).attr('name').split('.'),
                key = keypath.pop(),
                item = json;

            for (var i=0, l=keypath.length; i < l; i++) {
                if (!(keypath[i] in item)) {
                    item[keypath[i]] = {};
                }
                item = item[keypath[i]];
            }
            item[key] = $(this).val() || null;
        });
        return json;
    };