HTTP vs HTTPS performance comparison

Google recently announced that they will be starting to use HTTPS as a ranking signal in their search algorithms. This means that websites that serve traffic over HTTPS with secure, encrypted connections will be slightly favoured over those websites that don't. In my mind, I have always associated HTTPS with slower page load times when compared to plain old HTTP. As a web developer, web page performance is important to me and anything that will slow down the performance of my web pages is a no-no.