This feature adds an hyperlink to the Settings page of your SharePoint site. When clicking it, a page with detailed information about the site properties is displayed.
You can read detailed information about this feature here.
You can download the feature here.
Remark: The U2U Site Properties feature previously was part of the U2U SharePoint Solution Package. If you installed this solution, you will have to retract and delete this solution before you can install the new solution. The other features like U2U CAML Query Builder and U2U List Properties will be available soon in separate solutions.
Update 5/10/2007: you can download a new copy solving problems with the Event Receivers and the SPModulePropertyBag.