The ability to have a skin applied to your account, it is downloaded locally for the user.

Skins could be submitted to the server, and if a user selects a skin, then it is downloaded locally. When the client checks for updates, it can also check if the skin has been updated. If, when logging in, the skin does not exist locally, it is downloaded. This way there is a central skin repository and skins are kept up to date, and not loaded from the server every time.