So we could make a sitemap specifically for attachments such as images. Since this is a very special thing and only ever useful to forums that work a lot with attachments (such as photography forums maybe), it could be a setting that defaults to off.
Google supports image and video types in Sitemap now
http://googlewebmastercentral.blogspot.com/2010/06/sitemaps-one-file-many-content-types.html
So we could make a sitemap specifically for attachments such as images. Since this is a very special thing and only ever useful to forums that work a lot with attachments (such as photography forums maybe), it could be a setting that defaults to off.