Surgery that occurs on the wrong patient, or on the wrong side is apparently a lot more common than reported in the medical literature. According to the Archives of Surgery, in fact, you'll read more about it in the general press than in the medical literature. (They appear to attribute that fact to "shame.")
The article suggests that surgery on the wrong patient, or the wrong side is preventable--I sure hope so! The researchers looked at several databases demonstrates that WSPEs occur across all specialties, with high numbers noted in orthopedic and dental surgery.
Here's a web site I found that's devoted to this form of medical malpractice. Here's what on doctor says about the study and how he prevents wrong sided surgery from happening to his patients.