When you install any Adobe CS5 Suite or Point Product, the third-party Growl notification system and Growl system preference pane are automatically installed. Adobe says this was done to provide the user notifications reminding them to register their product. Because the Growl is an independent system, once install it will prompt users to install updates, and this is typically when users discover it was installed in the first place.
Adobe has gotten a lot of negative feedback about this, and in retrospect they have stated “We realize that this is causing a lot of consternation with both CS5 and Growl users. We should have been more transparent and made Growl an optional install. We made a mistake and are actively working to mitigate the problem.” http://blogs.adobe.com/oobe/2010/05/growl_installation_with_adobe.html
The developers of Growl have also posted this message on their homepage “If Growl was installed on your system without you knowing about it, please see this page for an explanation”. They subsequently say “We do not endorse applications installing Growl without your permission. In fact, we hate it. Nothing should ever install anything on your system without your knowledge and your explicit consent.” http://growl.info
Adobe has posted details on how to remove Growl or disable notifications to this site, which has no impact on how CS5 applications work… http://kb2.adobe.com/cps/840/cpsid_84093.html