[quote=@Revans Exile]
Tags are to threads as bumper stickers are to that car.
[/quote]

I snickered. I can see where you're coming from, though. Archive Of Our Own has tags. Most times, these tags help people find stories they want. Other times, the tags contribute nothing more than mere "comments", much like Tumblr or as you pointed out, bumper stickers. 

However, with enough moderation, I could see the tag system be used at a healthy degree.