JavaScript and HTML5 local storage for trivial customization in order not to ruin cache

https://youtu.be/gBT4uxtSkFY?t=540

Video: "Django under massive loads - Christophe Pettus - PyConAr 2012".

Starting at 9:00.

The lecturer said that one of the worst things that ever happened from the performance point of view on the web is putting someone's last name at the upper right corner. It's a perfectly static page. Nothing changes. But the name breaks the staticness of the page.

And the lecturer suggests to use JavaScript and HTML5 local storage for such trivial customization as adding username to the page.

I've tried to find more information on this technique. But failed.

Could you tell me where to read about this. I'd like to find it chewed over in an article. Could you give me a kick here?