TL;DR If you use “Vary” to negotiate content, the responses will fight for the same cache space. Additionally, IE ignores “max-age” and Safari is buggy.
Every mobile browser has a feature area where it outperforms other browsers by a factor of 10–40x. The Surface outperforms the iPhone on SVG by 30x. The iPhone outperforms the Surface on DOM interaction by 10x. There is significant room to further improve purely from matching current best competitive performance.

Michael Mullany, 5 Myths About Mobile Web Performance

This blog post from Sencha has been making the rounds recently. There are a bunch of interesting little tid-bits in there and I’m glad to see these kind of research results getting published.

(An an aside: they need to do something about their graphs. It’s nice that the surrounding text provides the context but the axes are unlabeled and there are no titles. Oh well.)

The abstract from this recent Nicholas Zakas talk:

After consulting with several companies on performance related issues, it became clear that one of the biggest performance issues facing websites today is the sheer amount of JavaScript needed to power the page. The demand for more interactive and responsive applications has driven JavaScript usage through the roof. It’s quite common for large sites to end up with over 1 MB of JavaScript code on their page even after minification. But do today’s web applications really need that much JavaScript?