On the Ibuildings site there's a tutorial posted talking about working with entities in Drupal 7 and how creating your own classes for them can make them easier to manage.

Developers love object-oriented code. But how can this be achieved with Drupal 7 entities? By default Drupal uses a single class for all entities of a given type. For example, all node objects are standard classes (stdClass) and all entity objects have the Entity type. I personally like to have an entity model that only exposes the functionality that is applicable for the logic of your domain.

[...] Wouldn’t it be nice to create your own classes for entities?

First off, he starts with a refresher on what entities are and how they relate to the database schema. He points out the difficulties in using them and testing their types. He then provides his suggested solution for "all" of your entity problems - the creation of classes for the different entity types. He gives an example using an Article type and how to create/use them in your Drupal code.