Here is a short summary:
- Nested Classifiers: This is an extremely powerful concept. In UML, almost every model building block you work with (classes, objects, components, behaviors such as activities and state machines, and more) is a classifier. In UML 2.0, you can nest a set of classes inside the component that manages them, or embed a behavior (such as a state machine) inside the class or component that implements it. This capability also lets you build up complex behaviors from simpler ones, the capability that defines the Interaction Overview Diagram. You can layer different levels of abstraction in multiple ways: For example, you can build a model of your Enterprise, and zoom in to embedded site views, and then to departmental views within the site, and then to applications within a department. Alternatively, you can nest computational models within a business process model.
- Improved Behavioral Modeling: In UML 1.X, the different behavioral models were independent, but in UML 2.0, they all derive from a fundamental definition of a behavior (except for the Use Case, which is subtly different but still participates in the new organization).
- Improved relationship between Structural and Behavioral Models: UML 2.0 lets you designate that a behavior represented by (for example) a State Machine or Sequence Diagram is the behavior of a class or a component.
http://www.softwarestencils.com/uml/index.html - Addons for Visio