My Weekly Update advises Yahoo to concentrate more on its own content and less on building out an ad network, but that’s because Yahoo needs to concentrate. Ad networks can be good businesses, especially when they can do some focusing themselves, and not just compete with Google and Facebook for remnant display inventory. Two examples of such differentiation come from Glam Media and Federated Media. AdAge thinks Glam is going public in Q2, and has a profile on its mostly women-centric approach. Federated’s John Battelle talks about turning a blog network into a conversation platform in this interview on McKinsey’s CMO site.