I don't understand the logic behind this. If a notification pops up and I want it to stay a little longer, I can hover it, but the notification fades, which makes it illegible. On the other hand, when I want to close it immediately, I expect it to close when I click on it, but instead it sticks even harder.
It seems like the logic is reversed here. Can it be changed ?
This is the design specification.
I can't find the original text to this, but as far as I can remember, the idea with the translucence on mouseover was designed so when a user needs to read what is below the bubble he/she can uncover it with the mouse pointer.
The Notify-OSD has changed a bit since this document appeared. Notably there are no more buttons on it. But the rational behind it is still the same.
However, I haven't seen a way to configure it as per your description. You would probably have to go to the source and create your own version.
EDIT
Webupd8 has an article how to patch the Notify-OSD to be click-closeable under Ubuntu 12.04.
