I know it's weird to go through slides of a presentation outside of the context of a real talk (and pales in comparison to the experience of being there) but nonetheless, there may be bits of goodness you can extract from them.

[Slides are embedded, come to site to view them or view on SpeakerDeck]

These are my slides from InControl 2012 where I did a talk I called "What We Don't Know" sort of based on this post. Here's the short of it:

On any given request for our website there are many unknown factors. One of the more obvious unknowns is the browser. There are lots of techniques and tools we can use to ensure good experiences across any browser. But we also don't know about the person. Who are they? Where to they live? What are they thinking? We should be admitting that we don't know those things either. And how does that person interact with their browser? And how does that browser interact with the server behind our website? These are all unknowns. The first step is admitting it and the next is embracing it.