Todd Hoff at High Scalability – Latency is Everywhere and it Costs You Sales - How to Crush it:

"In one of Greg's slides Google VP Marissa Mayer, in reference to the Google results, is quoted as saying "Users really respond to speed." […] Yet for some reason latency isn't a topic talked a lot about for web apps. We talk a lot about about building high-capacity sites, but very little about how to build low-latency sites."