Threads bumped to the top when somebody replies
Rather than having popular threads sinking to the bottom, I would rather keep discussions in the forum more active... This will help popular questions get read and not asked repeatedly, if DuoLingo puts in a sort questions by rating option to complement this.
A well signposted "technical help" area might also help. There are some very interesting site-development and translation process threads around, but they keep getting swamped by yet more threads on "Oh noez, my sound isn't working".