I'm using Snow Leopard, and at the time it was updated to 10.6.3.
I wonder if this is a problem specific to the Una and Mega boards, or if boards with FTDI usb to serial interface chips also had this issue? I would also like to know if the reported problems have been from folks like myself who use usb 1.1 hubs, or are usb 2 hubs also not working correctly in some cases?
I find it odd that a loopback test works just fine, but uploads to the Arduino fail. It doesn't seem likely, even with a keyboard and mouse connected, that even a limited 12mbps usb hub's bandwidth would be maxed out by a 19.2 kbps serial connection. I mentioned earlier a possible need for firmware updates on the 82U, but it seems almost as likely that the boot program on the 2560 could be at fault. I am a bit of a noob with the Arduino, so maybe I'm just blowing smoke here, but it doesn't seem to add up that a loopback test should work fine, but transferring the program to the Arduino fails. If I get some extra time, I may write a script to transfer more substantial amounts of data over loopback and see if it still holds up.