Trulia and Zillow announced they will join forces in a deal worth a reported $3.5 billion. It looks a lot like something that happens in tech when a sector matures in which companies start buying each other open a so-called roll up. We explain why this happens and what to expect in this business. Plus, Dollar Tree will also be acquiring Family Dollar Stores in a deal valued at $8.5 billion. How have things changed and how are these stores repositioning themselves as the economy recovers? In Detroit, the city water agency is proceeding with its plan to go after individual residents who are delinquent, to scare people into paying up, while negotiating with or otherwise letting slip by the big delinquent users who can fight back. Like Chrysler. And the state of Michigan.