Hi Ginger,
Actually - ran into the same problem today. I used this post to fix it.
The lockup happened while reading Dorian Gray. I was adding a note to a bookmark - when I switched to symbols mode - locked up. I connected it to my Mac (without rebooting to Windows) - and the USB Connected thing came up. Unplugged it - and voila.
It seems connecting it is the Sony equivalent of ctrl-alt-del. I don't think plugging it to the wall charger helped because the wall charger is a straight pass through - no attempt by the computer to perform a "mind-meld" with the device. Theoretically it is not good to plugin and un-plug a storage device without properly ejecting it - but, I am pretty sure the device doesn't use a platter style drive, and because no information was transferred - we should be good.
(I suppose one could also use the reset button on the back of the device; however, that might reformat the device - which is why didn't try that first.)
Cheers,
Josh