HTML5Boilerplate and others [edit] download jQuery in the way we all know:
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script>window.jQuery || document.write('<script src="js/vendor/jquery-1.10.2.min.js"><\/script>')</script>
Is this better for users? It’s good practice to keep DNS queries low, and if we don’t grab jQuery-UI or other frameworks from Google, then this is the only resource we get from their CDNs. Will service from our servers be faster?
Is this better for the server? How much do we really save by using the Google CDN just for this small file and not for serving it?
Why just jQuery? Why Google? HTML5Boilerplate includes normalize.css and modernizr.js, both of which are popular files (possibly more popular and more complex than jQuery [controversial] ) and are available at http://cdnjs.com/ and several other CDNs. If we load jQuery, why not those 2? Is jQuery loaded from the CDN because it is delayed to load at the bottom of the page, and therefore needs to wait for extra .1s to get it from the CDN? I know that Google CDN is a giant, but it is not unbelievable that other CDNs can handle a good amount of traffic.
Edit: After reviewing the code for this page itself, they use their own CDN for 10+ resources, and then use Google for jQuery. There must be a good reason for this, right?