[ricardobeat]

The Growl developers really messed up on this. Growl is now actually something that developers include in their applications, you don't need to install it at all.

You only need to install the app for backwards compatibility with apps that haven't upgraded. Since it was open-source, there is a fork that you can install for free: http://www.macupdate.com/app/mac/41038/growl-fork

[Karma_Police]

Well, you may still want it if you want to build some custom scripts that need notification, so the fork is probably your best option.