I hated when textbooks/papers did this. Half the time you can't tell if they meant to use the bold letter or if the printer was just being generous on that character. Made legibility quite a bit more difficult. BB letters are unambiguous.
For a good while, Yik Yak was very popular on my campus. Then when handles became mandatory, basically everyone stopped using it. Even after they back-pedaled, though, our feed was merged with several in the surrounding area, so we lost the sense of community we had with it on campus, and it never took off again.
I don't know about overall, but in my social microcosm yik yak was never able to recover its lost users.