User moved to a new usergroup upon purchase.
A shopping cart supporting paypal and google checkout.
Options for a branding free download and a required field for supplying website of product use upon purchase.
Downloadable area in user profile for skins purchased.
Adding skins via admincp should require server direct path link instead of actually uploading the file, files will be placed behind public_html.
Download link in user profile should be something like google.com/somefoldername/skinname-USERID#.rar even thou themes are hidden behind public_html.
When viewing a users profile via admincp, a checkbox option should be available which controls the downloads they have access too.
I'll try to create some screenshots of a few of these options with photoshop within the next day or so. PM me if you are interested.