You can also copy WBS, a group of WBS, an activity or a group of activities from one project to another. Some create template projects for this usage. You can also save lists of activities in an Excel spreadsheet and import them into an existing project. As mentioned above by Authur, you can also use the Methodolgy Management module aka The Project Architect to do this as well. Primavera P6, as you can see, gives you a lot of tools to perform the fragnet function.