My favorite site on the web is The Baby Name Wizard. By Common Consent is number two. Recently, they added a new feature that maps popular names in each state over the course of several decades. The surprising result: Utah is often the state where baby name trends are incubated. Check out Natalie, Madison, Jacob, and Jayden on the map.
This post mostly exists to share a cool site. But there is also a wealth of information here about how names spread and people interact. Some names become popular in regions; others hit the national scene immediately. Madison is popular everywhere but Wisconsin. Who wants to name their child after Madison, Wisconsin? Dakota, for boys, never became popular in the Dakotas. On the other hand, Caroline has been popular in the Carolinas.
So enjoy exploring the site, and feel free to speculate in the comments about why Utah leads so many trends.