Before I knew the word “UI” even existed, I loved making skins for Winamp and various other applications (my 2004 skin, Impulse[1], still shows up on their site). It was a fun, approachable way to create functional pieces of art, and in retrospect taught me a lot about creating a product from start to finish. It was exciting to make something in my bedroom that hundreds of thousands of people around the world would use.
Saddest to me, is that I can’t think of today’s equivalent, a widespread and useful app that encourages its users to tinker and easily modify the interface.
Perhaps Tumblr to a certain degree? I've met some young front-end guys that cut their teeth making Tumblr themes. I suppose what you can modify with Tumblr Themes is more limited than winamp skins.
Saddest to me, is that I can’t think of today’s equivalent, a widespread and useful app that encourages its users to tinker and easily modify the interface.
[1] http://www.winamp.com/skin/impulse/142212