wiki.user.js

// ==UserScript==
// @name           Hide banner in wikipedia
// @namespace      wikipedia.org/
// @include        http://*.wikipedia.org/*
// @match          http://*.wikipedia.org/*
// ==/UserScript==

if (typeof hideBanner == "function") {
  console.log("hiding banner");
  hideBanner();
}

// thx http://stackoverflow.com/questions/2246901/how-can-i-use-jquery-in-greasemonkey-scripts-in-google-chrome
function addJQuery(callback) {
  var script = document.createElement("script");
  script.setAttribute("src", "http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js");
  script.addEventListener('load', function() {
    var script = document.createElement("script");
    script.textContent = "(" + callback.toString() + ")();";
    document.body.appendChild(script);
  }, false);
  document.body.appendChild(script);
}

// remove SOPA banner 
// XXX: check for en.wikipedia.org url?
addJQuery(function() {
	setTimeout(function() {
		if ($("#mw-sopaOverlay").length != 0) {
			$("*").show();
			$("#mw-sopaOverlay").hide();
		}
	}, 500);
});