In Keys to a Fast Web App I listed caching as a big performance win. I’m going to focus on caching for the next few months. The first step is a study I launched a few days ago called the Clear Browser Experiment. Before trying to measure the frequency and benefits of caching, I wanted to start by gauging what happens when users clear their cache. In addition to the browser disk cache, I opened this up to include other kinds of persistent data: cookies, localStorage, and application cache. (I didn’t include indexedDB because it’s less prevalent.)
http://www.stevesouders.com/blog/2012/09/10/clearing-browser-data/