A common misconception is that Core Image is basically Quartz Extreme Extreme. This is not the case. Core Image is only a set of filters, similar to the filters in Photoshop, which OS X provides as a framework for developers and are rendered in real-time on the GPU. Core Video is the same, only with video.
What this means is that you could soon see some reasonably cheap alternatives to Photoshop. The main problem with creating a Photoshop is that it takes a LOT of time and money to write the pixel-level code necessary to create its filters. With Core Image, the work's already been done. Of course, there are other applications that could use Core Image, as it is not limited to editing documents, but this example is the one that springs most readily to mind.