If you have subgroups, you can now put them into categories. In the Subgroups page under Admin, click the new Categories button at the top. You can define categories and specify the ordering of them. Then, in each subgroup's Settings page, you can specify which category that subgroup belongs to.
You can specify that a person can only belong to a max number of groups within a particular category.
As part of all this, I revamped the Subgroups listing page, which is where these categories will show up.
Please let me know if you have questions or suggestions for improvements (which I'll get to after I'm back from vacation).