How to detect jQuery $.get failure?

You’re right that you can use jQuery 1.5’s new jqXHR to assign error handlers to $.get() requests. This is how you can do it:

var request = $.get('/path/to/resource.ext');

request.success(function(result) {
  console.log(result);
});

request.error(function(jqXHR, textStatus, errorThrown) {
  if (textStatus == 'timeout')
    console.log('The server is not responding');

  if (textStatus == 'error')
    console.log(errorThrown);

  // Etc
});

You can also chain handlers directly onto the call:

$.get('/path/to/resource.ext')
     .success(function(result) { })
     .error(function(jqXHR, textStatus, errorThrown) { });

I prefer the former to keep the code less tangled, but both are equivalent.