I think this visualization could be nicely completed by community labels. To go on with the city metaphor, you could have a road sign for each cluster of buildings. I can count 10 big community in the StackOverflow metropolitan area. A modularity algorithm would identify these clusters. Then you could get a list of most frequent tags in the users of the cluster to build the road sign.
Money isn't everything -- but it's a long way ahead of what comes next. -- Sir Edmond Stockdale