when plugged on my macbook pro, my arduino UNO is powered, but does not show up anymore: no dialog box for a new network device, nothing in /dev/tty* etc. Same behavior with my USBtinyISP: nothing in /dev, in "Usb Prober.app", console.app, dmesg etc.
After a lot of research on various forums, I ended up to this page: http://mightyohm.com/blog/2010/09/improved-firmware-for-usbtinyisp-fixes-usb-issues-in-virtualbox/ . Basically, the USBTinyISP was not working when connected directly to a USB port. But it would work if it were connected through a USB 1.1 device, such as a keyboard or a hub. I tried to connect the devices through a keyboard connected to my mac: both the USBTinyISP and arduino worked as expected.
My guess is that the problem and the solution is the same than the ones exposed in the above page: the USB stack on ISP and on the arduino is buggy. The code is supposed to be based on this one: http://dicks.home.xs4all.nl/avr/usbtiny/. This has evolved to version 1.6, while as far as I understood it, the ISP and arduino is based on an older one (back to 1.3, as usbtinyisp?) (is it this one ? : http://www.wulfden.org/TheShoppe/freeduino/ADABOOT.shtml).
So my question is: what is the firmware that is burnt with the arduino when I use the command on the IDE ? If it's outdated, do you plan to change it in the official firwmare ?
Again, this may explain why it does not work on my mac (and maybe others), but I'm not sure.
I would have like to update the firmware on my USBTinyISP to check if that would make it work, but I have no other ISP to program my ISP, and I'm not sure about how to do that. Plus, the adafruit web site says explicitly that no post about how to burn the firmware is allowed on the forum sigh. Still, there is a thread about a new firmware on the adafruit website: http://forums.adafruit.com/viewtopic.php?f=20&t=22436&start=0, but it has not been updated since.