Yes, it does sort of contain the idea that he didn't know at all about something. But this expression is used in a particular context. It is used to remark on the fact that a person committed some action while entirely unaware of what was going to happen next, or what he was getting himself into. The "little" that the person knows really implies that they could not anticipate the outcome or the consequences. "Little did he know, when he started his journey, how difficult it was going to be." "When he asked the beautiful woman for directions, little did he know that this simple question was going to connect him with the love of his life." "Little did he know that he was about to embark on the most thrilling experience of his life." "Little did I know that John was going to become such a great employee."

If you want to express the idea that someone doesn't know very much (or even anything at all) about a particular topic, you would say something different. "He knew little about forensic science when he started writing his mystery novel." Not the same as: "Little did he know, when he started his mystery novel, how much research he would need in the field of forensics." "She knew little or nothing about computers before she bought one." This is not the same as: "Little did she know, when she bought a computer, how much time she would end up spending on line." http://answers.yahoo.com/question/index?qid=20090512020404AAKlhR6

Little did I know, but..... It means you're admitting that you knew very little about what is about to be said. The rest should be clear from the context.

'little did I know' means "I don't have any idea at all (about something)." or "totally unaware of something." I just remember the Cascade's hit 'Rhythm of the Rain': "...but little does she know that when she left that day, along with her she took my heart." :)

didn't realize before, but now you do