I hate to be negative about this but this certainly doesn't seem comparable to either OneNote or EverNote. Both of these products seem far superior to this.
On Mountain Lion, we use the Notification Centre by default although you can opt to use Growl if you would prefer. In Lion, only Growl is available (obviously) :)
That's cool, if you happen to have the web app open. With Noti, the app just runs all the time (out of the way) and lets you receive messages at any time.
(Disclaimer: I wrote Statytus)