@Pertinax
Well, I can't say for anyone else, but for me it's the batch processing of images. Using the included "AutoFX" and ARexx command recoreder, you can change "I have to spend several hours doctoring up a dozen photos" to "Give me five minutes to set up ImageFX."
While I don't use the animation, I've heard that the biggest thing in IFX 4.5 is the keyframed animation brushes and all those nifty special effects.
