In response to your email:
1. We will use groups to be able to see the status of a particular "system." For example, we have an Internet facing portal called MyScouting. There are a lot of servers, services, applications, etc that make up the MyScouting portal. I would create a group and add all of the different components (and there are many) to it, so at a glance we can see the status of this portal. We have quite a few "systems" that are similar to this.
2. Configuring groups is easy enough. I would like to see the available object pane be wider by default. I know you can drag it to make it larger, but it would be nice if it was bigger by default. I also noticed when you go to manage groups, the menu bar disappears. The tabs are still there and if you hover over them, the menu bar comes back until you move off the tab.
3. I can't really speak to performance as the server I'm testing on only includes a handful of objects, unlike our production Orion server.
4. The group resources are on par with the other Orion resources. None of them were confusing, but it did take me a minute to realize that you have to edit the "Groups with problems" resource to only see specific problems, otherwise everything shows up there.