Ribbon

There are seven tabs initially but additional tabs can be displayed depending on your personal PowerPoint Options.
These tabs will look different depending on how wide your Word application window is. Every tab is divided into "groups" and the name of these groups is displayed at the bottom.
As you make your application window wider, more and more of the commands will be displayed until eventually every command from every group is visible.
In addition to these seven tabs there are also additional contextual tabs which automatically appear depending on what is currently selected.

The Close window in the top right corner of 2003 has been removed.
The application close behaves the same in both 2003 and 2007

Type a question has been replaced with a blue question mark in the top right corner.