87% of the time it takes to load a web page happens in the front end. This it taken from actual measurements of the top 50k websites. When we want to look for ways to speed up our sites we should look to where most of the time is occurring. At DrupalCon Denver I presented an introduction to front end performance in the session Faster Mobile Sites. This introduction talked about why front end performance is important, covered some details about what's technically happening, offered some simple solutions to get going, and talked about some useful tools.
The slides cover most of what I talked about. They were more than an aide to the presentation since many people don't watch the presentation videos.
If you have trouble with the video it is up on Blip.