I joined tumblr because, like you, I had a fandom, Fringe, that was not very active on LJ/DW. Suffice it to say that I learned tumblr is fun if you stick to graphics and gifs, but terrible for discussion. To this day, the majority of the conversations over there give me a headache.

Hmm, that poly relationship and other things you mentioned about Black Sails sounds very appealing.