This illustrates how Microsoft has taken User Interface development down a very bad path.
The original Mac OS UI standardized on a single location to find actions: The Menu Bar. Whatever you had to do, you knew where to look. This was in direct contrast to command line applications where you either had to keep the commands in your head, or look them up in documentation. Now, we have a proliferation of places to look for actions in a graphical interface: Menu Bar, multiple Toolbars, contextual menus, etc. This proliferation of places to look for actions is leading to greater UI confusion, and back to the UI problem of command line applications, as evidenced by the poster who didn't realize there was a way to mark an email as 'read' in the new Hotmail. The graphical interface is supposed to show you what you can do, you're not supposed to have to 'just know'. I find contextual menus particularly egregious, as there is no 'affordance' to indicate to the user that there's anything to look for. Does one just randomly right-click on everything to see if it has a contextual menu associated with it? Bah. UI design at its worst.
Unfortunately, due to the monopoly position of Windows, even the Mac OS has been forced to go down this path of providing toolbars and contextual menus. One mitigating trend I've observed in some (not all) Macintosh software is the use of contextual menus to duplicate operations presented in the menu bar.
UI design needs to return to a single canonical location to find operations (the Menu Bar). If UI designers want to use Toolbars and contextual menus, use them only as shortcuts for operations that are already presented in the Menu Bar.