When creating new source files xcode adds comments with your name and company name.
Where do I set my company name for xcode (not the project).
Adding to what SLF wrote above:
in Xcode 4 GM seed:
in the navigation pane (far left side), select the project (top item).
Expand the Utilities pane (at window top-right, far right button in the 3-button "View" group).
In the "Project Document" section is the "Organization" text field (File Inspection view, second section from top).
But there is a small catch:
Changing the Organization name as SLF described didn't set the project file as modified and no changes where saved.
You need to make a small change to the project, like adding a group after you change the organization name, this will cause Xcode 4 to save the file.
Also if you are working on a workspace, you need to make the change for each project.
Tested at XCode 4.0.2