Luca's Mac goes to sleep and goes into hibernate mode. Is that normal? Leo says it is and he can't turn off hibernate anymore in OS X. Will it hurt anything? Leo says not at all. It's designed that way. The sleeping computer refreshes the RAM and still checks his mail, syncs to his calendar, etc.
According to the chatroom, he can turn it off with a terminal command. Check out this Apple forum post for more info.