Haven't thought about power... I don't really want to use batteries because.. well.. 2or3 AA batts per module x 60 modules starts to get expensive/annoying battery-wise.

If the modules are going to be contained inside datacenter racks... then why no use USB power? They will only use a small amount of current (much less than the 500mA limit for USB) and USB ports will be wide available. External PSU jack can also be added.

 - "Security" might be a concern with USB-attached devices so the modules will only use the USB power lines. D+ D- won't be wired at all. This will isolate any "interference" between the arduino and the server/computer.