Back in 2010, Google announced that they are using site speed in web search ranking.
Speeding up websites is important – not just to site owners, but to all Internet users. Faster sites create happy users and we’ve seen in our internal studies that when a site responds slowly, visitors spend less time there. But faster sites don’t just improve user experience; recent data shows that improving site speed also reduces operating costs. Like us, our users place a lot of value in speed – that’s why we’ve decided to take site speed into account in our search rankings.