I don't know if this has happened elsewhere but here at work we have 3 dual 2.5Ghz G5's and 4/400Mhz G4's. The 3 G5's are obviously using OS X and 2 of the G4's are on OS X. The issue here is that in order to do anything on the G5's and 1 of the G4's the Server has to be mounted, the server being a dual 1Ghz G4 with Panther Server edition. If the server is not mounted and you try to do anything, including simply opening a window the beach ball of death comes up and it never goes away, but if the server is mounted first then everything works fine. They are all connected to a hub and networked to the buildings network in that way, but the hub is the only thing between these computers.