Activation of Adobe Photoshop CS4 adds a line of text to the "hosts" file found in the folder C:\WINDOWS\system32\drivers\etc. If the same line of text was added to the hosts file by another adobe product, activation may not be needed for further installations of Adobe products.
One other thing. When I opened CS4 and clicked on Help, one of the options in the drop-down menu had the word Deactivate. That suggests to me that the program was indeed activated.
If you decide to uninstall CS4, you need to Deactivate the program before doing the uninstall. If you fail to deactivate CS4 before running the uninstall, you will
not be able to reinstall CS4 on the same computer.