Tag this, tag that, tag tag tag!

Just about every online app now days has a place for tags.  In blogger, they're called "labels".  I think many people, myself included, use tags incorrectly.  For example, I'll often tag posts or videos with words I've already used in the post or video title or description.  That's dumb, since those words will probably get indexed anyway for search.  I'm going to start trying to tag my posts and videos along the lines of "categories".  Like, "howto", "gadget", "review", "instructional", "observation", "dogs", "pets", "programming", etc.  I think a tag should be metadata that describes what the content is about, not a rehash of the content.