Very good. Good for religion, ancient history, early modern history... these are my experiences. Sometimes I'm disappointed with some of their edited books (of compiled essays, that is), but I think this might be because I'm comparing these works to some of the superb reference materials or textual studies that they have, apples and oranges style.
This might interest you:
http://chronicle.com/forums/index.php/topic,22444.0.html