I'm a big fan of sites that work really, really fast. Mostly because I know that a fast website equals happy customers and happy customers equal increased revenue. One of the things that High Performance Web Sites suggests is reducing the total number of requests a site make so the user's browser spends less time communicating with your server and more time having your users interact with your site. A quick way to do this is to offload jQuery to a CDN like Google so everyone can use the same jQuery file (I mean exactly).

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script src="//ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.min.js"></script>

The only downside to this is if Google happens to be down (which doesn't happen frequently) or your development computer isn't online (also not very frequent but still an issue) then your site is going to grind to a halt. In order to prevent that we can add fallbacks to check and see if jQuery has been loaded and if it hasn't we'll load the copy from our server.

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script>window.jQuery || document.write('<script src="/js-static/jquery-1.10.2.min.js"></script>')</script>
<script src="//ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.min.js"></script>
<script>window.jQuery.ui || document.write('<script src="/js-static/jqueryui-1.10.3.min.js"></script>')</script>

I've started adding this to every site I build now and it's great.