No employee works at 100% of his full time! From time to time, we send a personal e-mail or surf the web to grab personal data. CNet News released an interesting article about the cost of “fun at work” for a company.
Costs are not only due to employee no-rentability but also to all the countermeasures deployed to protect the company assets against threats created by people: E-mails, websites, files download, instant messaging, social websites, blogs, …
You’re right but company assets (workstations, laptops, …) cannot be used for “fun”. They must stick to the security policy. I prefer to set up a dedicated room to let employees to relax and play. In this room can computers be installed (and not connected on the corporate network) for funny or personal purposes. Of course, those computers must be protected against all well-known threats!