Hard one! It seems hard for designers of our time to imagine our everyday job without this tool. I'm sure I use it more than I notice. I mean each picture that I take from camera, on the web or from a scan is automatically opened in Photoshop. I would be curious to see how many picture files have never been opened in it.. But I believe we should always remember that this is only a tool that should help us to save time. I already incorporate a lot of my process without it, but I still believe it is essential.