Just bought a Cybook Opus this weekend and plugged it into my laptop (Windows 7). The reader was not recognized by Windows and even worse, the reader FROZE complety. Tried to reset but that didn't work. Eventually i disconnected the battery and that worked.
The reader was charging.
I've read somewhere that it could be a cable problem (cable was delivered with the reader) but i do not think that's it, because when I plugged it in at my desktop at work (XP) it worked perfectly.