Comment 1 for bug 1008182

The interaction-design (or rather non-interaction design) of desktop-notifications wrt to NotifyOSD (used in conjuction with unity7 on the current desktop) does explicitly not provide any means to allow/force the user to act on them (e.g. close them).

The notification-bubbles do not get in your way (they are click-through and "defocus" if you hover the mouse-pointer over them) to not break any workflow and interrupt your current actions (e.d. clicking button, reading text) with any UI-element, which might be below the notification-bubbles.

That's why it's marked as "Won't Fix". For reference, please read https://wiki.ubuntu.com/NotifyOSD#Rationale

The new notification-system (for unity8) revisits notifications and their interaction-design. Currently unity8 is only used on devices such as phones and tablets, but will make its way to the desktop too (keyword: convergence). As a glimpse of how it's going to look, you can watch...
http://www.youtube.com/playlist?list=PLXvTBWcnTI1M1n66KdFJRyakGlANTTbfQ