Delegate controls are a very good mechanism to replace an existing control with another control through a SharePoint Feature. For example a delegate control is declared as <SharePoint:DelegateControl runat="server" ControlId="SmallSearchInputBox"...

The default people search in MOSS refines search results based on Department and JobTitle. When a profile property is created it gets automatically added into the Managed Properties collection. If you need to refine people search by additional profile...