CS3 brought a feature called 9-slice scaling from Flash Professional into Illustrator. At that time, 9-slice was only really useful for Illustrator symbols after importing them into Flash. Now, in CS5, 9-slice works on the scaling of any symbol right inside Illustrator. Let’s say you want to make a button with text on it, but when you scale it up, you don’t want the text to stretch or the rounded corners to distort. Make the button into a symbol (drag it into the Symbols panel) and apply 9-slice scaling (select Enable Guides for 9-Slice Scaling in the Symbol Options dialog), then you can scale the button without distortion.