Another take on opening external links in a new window.

gistfile1.js

$(function() {

  // Get the current domain name without any sub domains.
  var internalDomain = (function () {
    var domainParts = [],
        hostnameParts = location.hostname.split("."),
        i;
  
    if (hostnameParts.length == 1) {
      return location.hostname;
    }
    for (i = 0; i < 2; i++) {
      domainParts.unshift(hostnameParts.pop());
    }
    return domainParts.join(".");
  })();
  
  // Regex for a full URL.
  var fullUrl = /^([\w]+:)?\/\/.+/i;
  
  // Regex for a full internal URL. (See this trick:
  // http://stackoverflow.com/questions/185510/how-can-i-concatenate-regex-literals-in-javascript)
  var internalUrl = new RegExp(/^([\w]+:)?\/\/[^\/]*/.source + internalDomain + /\//.source);
  
  function urlIsExternal(url) {
    return url.match(fullUrl) !== null && url.match(internalUrl) === null;
  }
  
  function checkLinkTarget(link) {
    var href = link.getAttribute("href");
  
    if (href && urlIsExternal(href)) {
      link.setAttribute("target", "_blank");
    }
  }
  
  // Process all links with a slight delay to minimize the performance impact.
  (function() {
    // All links without an existing target attribute.
    var links = $("a:not([target])", context).toArray();
  
    var processLinks = function () {
      checkLinkTarget(links.shift());
      if (links.length > 0) {
        setTimeout(processLinks, 10);
      }
    };
  
    processLinks();
  })();
});