One of the new features in Mountain Lion, the upcoming version of OS X, is Notification Centre. As Chris Herbert at Macstories explains:
Among these changes, and one of the most important pieces, is Notification Center. As the name suggests, it is basically Notification Center ported from iOS, running at a system level on Mountain Lion. Besides having the same UI elements we see on our iPads and iPhones everyday, it also has a badge mode much like Growl, our favorite open source notification system for OS X.
I like the concept of Notification Center on a Mac. It would be convenient to see all notifications in a single place and I can see that saving a bit of time. However, I'm not so sure about that badge mode a la Growl.
I installed Growl once and hated it after a few minutes. I found messages popping up on screen every time something happened extremely annoying. I can't think of anything that's that urgent that requires a bloody popup to interrupt what I'm currently doing. The only app that did that in my set up currently was Dropbox and I didn't like it, so I turned it off.