Good idea, nitro. I think it's a perception problem atm, because the current list of most used tags on the upload page isn't really helpful (and because they're exposed, they get used, while other tags are mostly ignored). I'd suggest gear, software, genre and mood/speed/pace (ie calm, dance etc). Also, to help building a DB, I think it'd be good to hard set the tags on the upload page and offer a selection for each category.
Also, I think we should allow listeners to add tags. The author has always the option to remove them by editing, and it's neat to see other people pigeonholing ones music.
And if you add multi-tag search, that'd be the icing on the cake.