i have a cybook gen 3 and it's never locked up or rebooted. also i love the mobipocket format because i can read it on my computer, pda, eee pc or my cybook. you can also very easily convert text files to work on the cybook, and a lot of older free books are offered in text, so that's very helpful.
learn more about the mobipocket reader here
http://www.mobipocket.com/en/Downloa...sp?Language=EN
and i see that they do offer a version for mac.