Private Messaging also gets my vote.
In addition to that I would like to see in the "My Skins" section of the user's profile the option to display a detailed list, i.e. similar to how individual galleries list their items, with screenshots and first few lines of the description.
Also I would like to see "skin subscriptions" - similar to how some forums have thread subscriptions, here you would subscribe to the skins. Subscribing would mean that, first of all, you could see a list of all your subscriptions, kinda like marking them favorite. However, more than that you'd be notified when one or more of the subscribed skins have been updated and/or have new comments.
