[wavded]

I had one more thought on this @danneu, I believe Growl stacks? I'm not a Mac user so I'm not sure if that is true. On Linux, Ubuntu libnotify does not, nor does Gnome Shell's notifications, two leading desktop environments for Linux and I've used both without having that desire for them to stack. Not saying stacking is not better, but I think its usable, and has its pros. E.g. how many should stack reasonably without being an issue, having a bunch stacked can crowd a portion of the screen. This lib may be able handle that in the future, but one of its strengths is that its easy for users to create vastly different themes partly because it doesn't stack. A relevant point of discussion however.