Here's the correct sequence to uninstall the CS3 beta and install the final, shipping version of CS3:

1.— DEACTIVATE the Photoshop CS3 beta;

2.— Run the Adobe Uninstaller currently residing in your ./ Applications / Utilities /Adobe folder to uninstall the Photoshop CS3 beta;

3.— Run the 'CS3Clean' script that has been posted to remove the bits and pieces that the uninstaller misses.

NOTE that you cannot just drag the CS3 beta folder to the Trash like you normally do with other Mac applications.

To install CS3:

1.— Repair Permissions.

2.— Install CS3 according to the instructions.

3.— Repair Permissions AGAIN.

4.— Activate the software.

here is the link to the clean script:
<http://www.adobe.com/support/contact/cs3clean.html>