I haven't made it entirely public (so far only Alf of the Tau mod and the Admins on Hangar-8's forums know about it) but Skins@HWT is gaining tags for its downloads.
All of the data isn't in place yet, but the initial functionality of a tag cloud is working, and once I have more data in then each download will show a list of its tags on the detail page.
For those who don't know what tagging is (probably those who haven't been near blogs) it's a very simple system for using key words to identify themes in content. Blogs use it to identify the content of posts, and Skins@HWT is using it to identify the content of downloads.
For now all you get is "click tag and see all content that has that tag" but in a future update "tag searching" functionality will be added that allows you to combine tags to say, for example, "show me all of the Chaos themed content that is compatible with Winter Assault that brings it more in-line with the codex" by selecting "Chaos AND WinterAssault AND Codex"
If anyone has any ideas on useful tags, post them here or give me a shout.