Once again, Apple Chief Executive Steve Jobs is taking medical leave for the third time since 2004 and once again, the company's stock price is unsteady as Jobs refuses to be forthcoming about the details of his condition.  It is probably connected to the rare form of cancer called a pancreatic islet cell neuroendocrine tumor that Jobs has suffered from previously.  Jobs had such a tumor removed in 2004 and said afterwards all the cancer was gone, and he did not require chemotherapy or radiation treatment.