On the following page:
Customers -> Manage Customers -> Click on a customer
It shows a list of tabs on the left side, one of which is called "Customer View".
But when I look at Mage_Adminhtml_Block_Customer_Edit_Tabs::_beforeToHtml, I see that the function call to addTab() is commented out for the "Customer View" tab.
So where is the Customer View tab being added from?