What is ajax.googleapis.com? I noticed it allows the like / dislike function to function. No reason for the question just bored as **** to be honest.
Its a set of rules for Javascript in effect. Its available from Google in an open source format so widely used by web designers and cms.
One thing it does is allow for in page refreshing without loading the whole document. Without it websites like BBC Sportsday or anything showing goal updates won't work (won't update anyway) you will have to press F5 all of the time.