Same issue for me, on Ubuntu Precise (12.04) and was already the same with Ubuntu Maverick.
Surprinsingly, when I boot with an SD card already in the slot, Ubuntu sees the SD card. If I remove it, then get it again in the slot, it works. In short, if there was an SD card at boot time, it's OK, otherwise, it is not.
Same issue for me, on Ubuntu Precise (12.04) and was already the same with Ubuntu Maverick.
Surprinsingly, when I boot with an SD card already in the slot, Ubuntu sees the SD card. If I remove it, then get it again in the slot, it works. In short, if there was an SD card at boot time, it's OK, otherwise, it is not.