It *should* auto-mount, but I've been having problems with my Kubuntu installation too.
In a terminal window type 'tail -f /var/log/messages' (you might have to be root depending on your installation). You should see a stream of messages when you plug in the Sony. When I plug in my PRS-600, I see three partitions, including the SD card. Try manually 'mount'ing the various partitions.
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