It responded but there was a very slight delay between the time I put my finger on the sensor and the screen actually being unlocked. (pokde.net)
I saw very slight delays when tapping the screen to open apps or visit a webpage, but I wouldn't call the experience slow. (zdnet.com)
Since there is a very slight delay in on - screen response to input (barely longer than the similar delay when using the physical keyboard on older Kindles) it can be slightly strange at first, but that fades quickly with continued use. (kindle-apps.net)