When I first got Winamp, I was really annoyed because I could never find skins that I liked, or even just skins of a particular series/actor/singer/etc. To satisfy my want, I decided to make some myself. Eventually, they just started to accumulate in a folder, and I thought I should share them with everyone else to help those whom were having a similar dilema. Plus I thought they were going to waste if I was the only one using them.
I usually only skin the three main windows (main, equilibrium and playlist) since those are the only windows I use. If any of the other windows are skinned, it will be noted in the description next to the skin's preview (which will preview whatever windows I skin).