well that wasn't exactly for the average user... let me try
CoreImage and CoreVideo provide hardware accelerated image and video processing. Look at it this way, your video card is GREAT at playing games right? It can process polygons and colors like mad to make those games look good (maybe not YOUR card but the new cards anyway). How would you like it if you could take that processing power and apply it to every day applications rather than just to games? This is exactly what CoreImage and CoreVideo do. They hardware accelerate certain aspects of your every day experience.
For example, say you're doing some image processing in photoshop. you want to add a cool effect but it's pretty processor intensive. using CoreImage this processing can be sent to a specialized processor... your graphics card! It's BUILT to handle images and the math related to editing and managing images. It's perfect for it. Same goes for editing a movie in iMovie or Final Cut Pro. You want to add effects or do things with Final Cut Pro and make your movies but you're tired of the waiting .. you can have the video card do the work about 20 times faster than your computer's processor could. It's really THAT fast. It's built for images, so why not throw some images at it? All that power and it's only used for games? Please, it can be put to good use all the time, and that is what Tiger is going to provide.
From a user perspective you will see faster usage in Image and Video related processing from applications that take advantage of it. From a developer point of view you have a lot more at your disposal to make really cool applications that just weren't possible before. There's a lot of power to harness there and Tiger will make it possible