Comment 3 for bug 184944

Your problem very looks like the bug I reproduced in bug 199215. Can you install all Hardy updates in order to have the latest kernel, install gparted (sudo apt-get install gparted), put a SD card that does not automatically mount, and then open gparted (gksu gparted) and look if your device is listed? If your device is listed in gparted, you can also let gparted automount your SD card to see if it successfully mounts.

In my case, I had the same problem than you, but it appears that the kernel correctly detects the device, but that the device is not mount automatically most of time, but still usable and mountable.