Nahuel Foronda has a post on stateful skins in the Flex 3.0, cool stuff that this has been added in Flex 3.0 beta 2, but not really biggy to re-create in previous versions of Flex 3.0.
Pretty pointless but all I did was copy all of Nahuel’s code (I had to change the paths to the images), and then just added a single switch statement.
Example here, right click for source.
I thought you’d be able to recreate this easily in Flex 2.0, but it becomes a pain because a Button in Flex 2.0 doesn’t have a ‘skin’ style. Creating your own button with this style should solve it though.