NeoCatさんの「JSONPのエラー検知（＆リトライ）可能版。」いいね！ http://d.hatena.ne.jp/NeoCat/20110206/1296934235 ※charset=utf-8だけ足した。

JSONP special

// Thanks NeoCat http://d.hatena.ne.jp/NeoCat/20110206/1296934235
window.xds = {
  	load: function(url, callback, onerror, retry, callback_key) {
			var ifr = document.createElement("iframe");
			ifr.style.display = "none";
			document.body.appendChild(ifr);
			var d = ifr.contentWindow.document;
			var cnt = 0;
			ifr[ifr.readyState/*IE*/ ? "onreadystatechange" : "onload"] = function() {
				if (this.readyState && this.readyState != 'complete' || cnt++) return;
				if (d.x) {
					if (callback) callback.apply(this, d.x);
				} else if (retry && retry > 1) {
					setTimeout(function(){ xds.load(url, callback, onerror, retry-1) }, 1000);
				} else if (onerror)
					onerror();
				setTimeout(function(){ try { ifr.parentNode.removeChild(ifr); } catch(e) {} }, 0);
			};
			var url2 = url + (url.indexOf('?')<0?'?':'&') +
				(callback_key?callback_key:'callback') + '=cb';
			d.write('<scr'+'ipt>function cb(){document.x=arguments}</scr'+'ipt>' +
				'<scr'+'ipt charset="utf-8" src="'+url2+'"></scr'+'ipt>');
			d.close();
			return ifr;
		},
		abort: function(ifr) {
			if (ifr && ifr.parentNode)
				ifr.parentNode.removeChild(ifr);
		}
	}