I had no problems with the Arduino (or, more specifically, with the FTDI drivers, as I have about 4 devices that use the chipset besides my Arduinos).
My problem was that when I upgraded my G5 imac from tiger to leopard, iTunes no longer saw my iPhone.
I mentioned this because it your problem seemed similar, and I've been doing computer support for enough years to realize that it's possible the Arduino is a red herring and not part of the actual problem, and maybe you really had the same problem I did if you've upgrade OS X lately.
Sorry, nothing to see here, move along.
-j