To emvie:
I tried to update the firmware again. This time it froze during the process and it was impossible to reboot the device. So I went to teknikmagasinet and spoke with the salesperson. He was not aware of any problem with the Readee since the new firmware is available. So, I'm not sure it'll be fixed any time soon
Anyway, I got a new one and it hasn't frozen while reading yet (it freezes however if I try to use bookmarks or recents). I keep my fingers crossed!