gistfile1.js

// ==UserScript==
// @name           Twitter Cleanup
// @namespace      Scrossics
// @description    Clean up Twitter's new "promotion" area
// @include        https://twitter.com/*
// @include        http://twitter.com/*
// ==/UserScript==


var divs = document.getElementsByTagName("div");

for( i = 0; i < divs.length; i++ ) {
  if(divs[i].className == "promotion") {
    divs[i].style.display = "none";
  }
}