I believe that GH should implement a top-level team concept. Having multiple teams pull from a single project right now is cumbersome. (See: http://jaibeermalik.wordpress.com/2010/07/22/using-greenhopper-to-manage-multiple-teams-in-agile/) This should not require custom setup to achieve. And it is frustrating our adoption.

Having separate project per team does not work either, as then there would have to be a separate "bug project" where issues could be reported but not associated with a team. Howver, then the coordination between what bug is in which project would be a nightmare. Enabling multiple teams within a single project, just like VersionOne and Rally is the right way to go.