A few suggestions:
Hook the blacklist lookup into Mr. Number or 800notes.com to help determine (along with existing community blacklist) whether to block a number.
Provide a way to either view the community blacklist, or show numbers that you have personally blacklisted which are now covered by the community blacklist. Since we only have a set number of blacklist entries, give us a way to find out which numbers we can clear out of our own lists once they are elevated to the community list.