When you create a new window system component (TopComponent) using the template wizard in NB 5.0 or greater, the default layout manager is BorderLayout, not GroupLayout (the new, super-easy-to-design-with layout manager in NB 5.0).
You can use GroupLayout if you want to - just right click the node for your component in the Inspector, and select Free Design from the Layout Manager submenu.
If you do this, your module will need to depend on the module that provides this layout manager. In NB 5.0 it is part of the ide6 cluster, which means it is not a part of the base NB Platform. Since many modules either only have one component in their TopComponents (a tree or a list or something), or embed GUI from some existing application, we didn't want to force every new plugin to have a dependency on the GroupLayout module whether they need it or not.
To add the dependency in NB 5.0 or greater, do not do anything! Just using the layout manager automatically adds the dependency on the library module for you. If you are making a platform application, rather than an IDE plug-in module, you will also need to ensure that at least this module is included in your application from the ide6 cluster. Cluster and module includes can be customized in the Libraries panel of the suite project's properties dialog.
GroupLayout may be moved into the platform module cluster and made the default layout manager in the future.
Source: NetBeans FAQ