I too put together a group report trying to get member stats. All I got was 100% availability for all menbers which I knwe was incorrect. I then put together a custom report using my custom properties and confirmed that some of my member nodes were 99.99xxx available. I contacted Tech Support and the Tech said he said he didn't use Groups but created his reports using custom properties due to these issues. It looks like in Groups might just round everything up.
Too bad. The group function would be a good idea if done properly.