$.get does not give you the opportunity to set an error handler. You will need to use the low-level $.ajax function instead:
$.ajax({
url: 'http://example.com/page/2/',
type: 'GET',
success: function(data){
$(data).find('#reviews .card').appendTo('#reviews');
},
error: function(data) {
alert('woops!'); //or whatever
}
});
Edit March '10
Note that with the new jqXHR object in jQuery 1.5, you can set an error handler after calling $.get:
$.get('http://example.com/page/2/', function(data){
$(data).find('#reviews .card').appendTo('#reviews');
}).fail(function() {
alert('woops'); // or whatever
});