Slate magazine has an awesome science section. Found this article in the section. Now I finally understand why I love Stumbleupon so much, even though I do not always spend time with the results of the stumble.
Research, as quoted in the article, has identified two distinct types of stimulation centers in the body - one that deals with seeking/wanting and another that deals with liking.
Seeking or wanting is the dopamine-based ultimate mammalian motivational engine. It is what makes us want to get up, seek, be curious, forage, crave, expect etc. Scientists have found that this is distinct and different from the opoid system of experiencing pleasure and satisfaction. In other words, the seeking system stimulates us to hunt, and the pleasure center makes us happy after success.
In human beings, the stimulation of the seek is stronger than the pleasure of success. Which makes evolutionary sense. Any animal with the pleasure center stronger than the seeking center quickly dies out, though completely satisfied. Humans, along with many of our contemporary mammals love the stimulation of seeking more than the satiation of success.
And that, ladies and gentlemen, is why I love to stumble so much. And you like to use Facebook, or twitter, or Google. Our evolutionary seek centers are driving us to distraction with the easily availability of the 'seek'.