Not a whole lot. I only watch what I'm very interested in. In all honesty though, the Muta thread is the only one the I really need the watch feature for. The others are just for convenience.
I usually leave non-Q&A threads on watch until they're featured/happeninged. Then I unwatch them until I remember they exist. I try to use the "news feed" by following users who I routinely make me laugh, but it's not great because it gets flooded by their sticker actions.