So I reserve the right to change my vote later, but for now, the top three CS4 features for me are:
- Illustrator's Blob Brush
- Photoshop's Quick Selection Tool
- Photoshop's Rotate View Tool
The Illustrator Blob Brush allows you to paint areas which immediately get converted to outlines. You can even use the eraser in combination to white out areas that have been painted. This feels much more like drawing with natural tools, but with the advantage of getting nice, easily manipulable outlines.
The Photoshop Quick Selection tool works the way you always wanted the Magic Wand tool to work. It just seems to know what you want to select. You can even drag it over an area to select all the parts that make up that area. You still have to watch what you're doing, but it seems to behave very well.
Photoshop's Rotate View tool is also long overdue. (Painter has had this for years.) Basically, you can simply drag to rotate the image in the window to get a more comfortable working angle. This is like rotating your paper on your drawing surface to get a better angle. Double-clicking the tool icon straightens everything up again.
I'm sure I'll be finding more as time permits, but these three alone make Illustrator and Photoshop vastly more useful to me.