I just downloaded the trial for Photoshop CS4 and am figuring it out. Those who have used it, please share what're the greatest new features that are useful for a photographer.
My fav features:
1) Content-Aware Scaling
Allows you to resize images according to the content. It keeps the important subjects as it is and scales the less important parts (such as repeated background).
2) Extended depth of field
Allows composites of multiple photos taken at different points of focus. Great for macro-photography when the DOF is razor thin. (tripod recommended if you're trying this) Its abit like CombineZM.