"The second (Stream) is called Sparks. In this feature, users type in subjects of personal interest — “sparks.” Then Google streams items about that subject. The content that Google pulls into your Sparks stream is different from the results you’d get if you put the same term into the search engine.
“It’s focused on getting stuff that’s fresh and social and fun. We’ve tried to tune parameters to get something that’s engaging,” says Andrew Tomkins, a top search engineer who joined Google after stints at IBM and Yahoo. The signals that Google looks for in determining Sparks content is freshness, a visual component — videos will rank highly — and the degree to which the content is virally spreading on the net. (Tellingly, the Google News group has moved into the Emerald Sea division.) In other words, Sparks tries to deliver the kinds of thing you want to share with others, and Google hopes that its users do just that."