Hi!
Here is the easiest way (but not the perfect one):
Go to the "Custom CSS" tab in the Back-end -> System Settings -> Look & Feel section. Tick the "Use custom css" checkbox and save the following code:
Code:
.product-details-tabs li.product-sku { display: none }
This will hide the SKU line on the product page from visitors, but will leave it in the HTML code of the page. That's why it is no the perfect solution. The best one would be creating a custom module that removes the SKU from the HTML code of the page.