>Content Delivery Network (CDN) Google and Microsoft are probably the most common.
>
>Replace the Url.Content() with the URL of the CDN you want to use.
>
Should it be

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.0/jquery.min.js"></script>
    <script src="//ajax.googleapis.com/ajax/libs/jqueryui/1.8.23/jquery-ui.min.js"></script>

    @*<link href="@Url.Content("~/Content/themes/base/jquery.ui.all.css")" rel="stylesheet" type="text/css" />

    <script src="@Url.Content("~/Scripts/jquery-1.5.1.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/modernizr-1.7.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery.unobtrusive-ajax.min.js")" type="text/javascript"></script>
    <script src= "@Url.Content("~/Scripts/jquery-ui-1.8.11.min.js")" type = "text/javascript"></script>*@

How about the css file for jQuery? It is not mentioned in that guide.