This is the reason for staff slacking off:

Google's mission: Google’s mission is to organize the world’s information and make it universally accessible and useful.

Facebook's mission: Facebook's mission is to make the world more open and connected.

What is yahoo? Yahoo! makes the world's daily habits inspiring and entertaining.  By creating highly personalized experiences for our users, we keep people connected to what matters most to them, across devices and around the globe.  In turn, we create value for advertisers by connecting them with the audiences that build their businesses.

http://yhoo.client.shareholder.com/faq.cfm

Note: if you do a google search for yahoo mission, nothing is found on yahoo itself. The lack of a big hairy goal is not motivating.