Brian Riggs from the Kiwi Project recently posted a must read article about loading Flex skins at runtime. This technique could have a lot of uses, as it may allow you to change the look and feel of your application without having to recompile the SWF file. Brian also has a great round up of Flex skinning articles.
My biggest beef with many Flex applications is that they look like, well, Flex applications. Without skinning and proper layout Flex applications look very generic and have the fresh “out of the box” feel. Skinning is one more way to make your application “pop” and leave people wondering which software which software was used. This is the feel I got when I first used Google Maps, I thought it was some new technology or even Flash at first. I think Flex has this same potential.