gistfile1.js

data = [
  {"created_at":"2013-03-07T12:24:06Z","id":49,"name":"Бегичева, улица","region_id":3,"updated_at":"2013-03-07T12:24:06Z"},
  {"created_at":"2013-03-07T12:24:06Z","id":359,"name":"Беговая аллея","region_id":8,"updated_at":"2013-03-07T12:24:06Z"},
  {"created_at":"2013-03-07T12:24:06Z","id":360,"name":"Беговая улица","region_id":8,"updated_at":"2013-03-07T12:24:06Z"},
  {"created_at":"2013-03-07T12:24:06Z","id":361,"name":"Беговой проезд","region_id":8,"updated_at":"2013-03-07T12:24:06Z"},
  {"created_at":"2013-03-07T12:24:15Z","id":3886,"name":"Беговая улица","region_id":115,"updated_at":"2013-03-07T12:24:15Z"}
];

data.forEach(function(element) {
  data.forEach(function(el) {
    if( element.id !== el.id && element.name === el.name) {
      element.conflict = true;
    }
  });
});

console.log(data);