Rhetorical questions can be overdone. A fellow attendee at a writing workshop removed all of the rhetorical questions from her novel and cut 2500 words. Writers tend to pile up rhetorical questions when a character is unsure, resulting in an overstatement of the problem. The reader understands that the character is confused after the first question. Adding three or four more is redundant.
Rhetorical questions can be effective if employed with a light hand. Use the search function in Microsoft Word to locate question marks in your manuscript. For every question that isn’t part of dialog, consider whether it can be cut or rephrased as a statement.
Please also see Mary Kole’s insightful post on rhetorical questions.