From the time I got my Kindle 2 with the 2.0 firmware, it didn’t mount except occasionally on my Mac. I was puzzled for a while, but I finally figured out what was happening. If you have wireless turned off, the Kindle 2 won’t mount on your Mac. If you turn wireless on and then plug it in, it mounts instantly.
My guess is that the Kindle 2 is trying to turn off wireless when it is already off, since it doesn’t get the turned off signal or whatever, it gets sort of stuck. The bug is still there in the 2.0.2 firmware.
I hope this helps someone!