BNB was great when it first started. I mean... heck, Waid and Perez!??!? I really enjoyed the way they passed a continuing story through a rotating group of characters (even into the future with the Legion of Superheroes).
Right now its very so-so, instead of rotating characters you get the Green Lantern and Phantom Stranger for three issues straight.
DiDio said some interesting things about the back up feature (and the selection of what goes where) in that 20 Questions 1 Answer (or whatever its called) on newsarama this week. Check that out.