As far as the RHB-500 goes, I have them in a star configuration, eight hubs connected to one root hub, all running off a single RaspberryPi w/MinePeon.
(Ignore the two empty hubs, I was preparing for some Blue Bitfury devices and moved 16 erupters to my test rPi, which is at my desk in another room, also for testing MineP
eon 2.4.0 pre-release.)
Also connected to the same rPi over proxy are the 4 blades which is off to the left.
(PS - Ignore the room color, lol, I haven't painted this room since I bought the house, I'm lazy...)