Comment by wycats

The premise is that jQuery 1.9 and 2.0 are API-compatible, so you can do something like:

    <!--[if lt IE 9]>
        <script src="jquery-1.9.0.js"></script>
    <![endif]-->
    <!--[if gte IE 9]><!-->
        <script src="jquery-2.0.0.js"><</script>
    <!--<![endif]-->

New browsers will get a lighter download and a faster runtime. oldIE will still work with all the hacks required to make it work.