In what has to be the most innovative use of social media, Digg Attack, a Javascript based 2D shooter game, uses the Digg API to create various anti-heroes characters that need to be shot down.
You start each level with a number of heroes (the little blueish dots). The game connects to digg.com and as stories are dugg, enemies are spawned and enter the screen from either the left or the right side. The type and number of enemies spawned depend on how many diggs the story has received.
Since it is a Javascript canvas based game, it works on Firefox 3, Safari and Opera, but not on Internet Explorer. (Thanks Ajaxian)