All I can tell you is that I had a couple off freezes in the old firmware version on PDF's he couldn't handle.
But now with the latest firmware PDF handling is much better and I haven't had a freeze since the update (which is exactly 1 month ago).
I must say that for 95% of the time I only read mobi-files and the mobi-reader on the cybook is very stable (as is the dictionary support).
So no complaints from me (knock on wood).
