Organic groups is a well used drupal module. I have been a fan of it for a long time and I am currently working with the module on one of my biggest projects so far.
The panels module is also a very popular module. Panels 3 is a stable version that you may use on production sites. Organic groups and panels together is a powerful combination. There is a dev-version of a module that gives you the oppertunity to tell a group that is shall have a default panel layout (withe predefined content set up by admin), a great feature that I think will be popular.
