Lara Hogan has just published her excellent book Designing for Performance for free online. She takes a good look at what makes a website feel slow and how that experience affects design and business goals:
Page speed is increasingly important for websites. If you’re looking for a page load time benchmark for your site, this is it: users expect pages to load in two seconds, and after three seconds, up to 40% of users will abandon your site. Moreover, 85% of mobile users expect sites to load at least as fast or faster than sites on their desktop. As you design and build a website, or as you examine your existing site, how are you stacking up against these expectations?
Lara is also donating all the proceeds from the book to excellent charities, so if you’re able, buy it.