@contextfree`: Can't agree.
Title bar: It's infinitely easier to "close" an application using the title bar due to the shorter mouse movement in a single direction. There are other ways this could have been accomplished as well, but this method is familiar and thus probably the best choice. The existing way you accomplish this with a mouse is horrible.
StoreApps on taskbar: Fewer mouse movements to access the apps.
Context menu on start screen: Doesn't go far enough... there should be context menus throughout. In any case, the benefit here for mouse users is locality. It's a lot easier to make small mouse movements than it is to make large movements. The context menu keeps the movements small, not requiring you to mouse all the way to the bottom of the screen. This may even make it easier to do some things with the keyboard, using the context menu key.
Shutdown on start screen: This one isn't for mouse users, but to simply make this very common task more discoverable. I'll be honest, I'm not sure I care one way or the other about this one, but this is something they've taken a lot of heat over, so I understand the change.
Boot to desktop: If you're a mouse/keyboard user you probably rarely need to go to the start screen. On Win 7 I very rarely open the start menu. So, for that usage scenario this reduces the amount of time and effort it takes to go from starting your computer to actually doing something with it.
Taskbar always available: I see the benefit of this for mouse users. Questions I have that could ruin this, though, include how it behaves for keyboard users and how it interferes with the command bars used by metro apps. I guess the same things apply to the title bar, but it seems much more questionable for the taskbar.