Nodes -- To what extent should they be used?

I'm considering moving from a custom php/mysql solution to Drupal, and I'm curious about how people are using nodes. My current impression is that anything can be a node (with some help from flexi-node). It makes sense to me that stories are nodes, but what about other resources? For example, my current system has people in one table, organizations in another table, stories in another table, and URL's in yet another table. I could see putting these different types of data into a single node table, but is that the most efficent way of doing it?