code:

// ==UserScript==
// @name           I'm Feeling Lucky!
// @description    Makes a link on the SA main forums index to take you to a random thread.
// @include        [url]http://forums.somethingawful.com/*[/url]
// @author         RedKazan
// ==/UserScript==

var looking = GM_getValue("looking",false);
var onPage = document.location.pathname.match(/^\/(\w+)\.php/i);
	
if (!onPage || onPage[1] == "index")
{
	GM_setValue("looking",false);
	var where = getNode(document,document,"//A/B[contains(./text(),'dreams come true')]");
	if (!where) return;
	where.parentNode.href = "#ClickHereForRandomThread!";
	where.parentNode.addEventListener('click',
		function (event) {
			var doc = this.ownerDocument;
			var links = getNodes(doc, doc.getElementById("forums"),
				"//A[contains(@href,'forumdisplay.php?forum')]");
			if (!links) { alert("This should not happen."); return; }
			GM_setValue("looking",true);
			doc.location = (links[Math.round(Math.random()*(links.length-1))].href);
			event.preventDefault();
			event.stopPropagation();
		}, true);
}
else if (onPage[1] == "forumdisplay" && looking)
{
	// Wait til the page fully loads so the client doesn't explode changing pages so fast
	window.addEventListener('load',
		function (event) {
			var doc = event.originalTarget;
			var table = doc.getElementById("forum");
			if (!table) { alert("Sorry bro, dead end."); return; }
			var links = getNodes(doc, table, "//A[contains(@class,'thread_title')]");
			if (links) doc.location = (links[Math.round(Math.random()*(links.length-1))].href);
			GM_setValue("looking",false);
		}, true);
}
else
{
	GM_setValue("looking",false);
}

function getNode(doc, context, xpath)
{
	var nodeList = doc.evaluate(xpath, context, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null);
	return nodeList.singleNodeValue;
}

function getNodes(doc, context, xpath)
{
	var nodes = doc.evaluate(xpath, context, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
	var result = new Array(nodes.snapshotLength);
	for (var i=0; i<result.length; i++)
		result[i] = nodes.snapshotItem(i);
	return result;
}