Okay. This may be a little jumbled as I try and get my thoughts in order.
While I was watching the crazy Desmond flashback episode, I came up with this theory. the book that was being auctioned off was said to be off the Black Rock and its contents were never revealed to the public. The guy said that previous owners was the Hanso family. The Hanso family was in control of the Dharma Initiative so I think that the journal had all the secrets to the island on it. So when Charles Widmore bought it, him and Penny found out all the secrets to the island which is why they both know about it.
And my theory about the oceanic six...
Faraday (the physicist) had asked if desmond was exposed to any high levels of radiation or electromagnetism. Who do we know so far are of the Oceanic Six? Hurley, Kate, Jack, Sayid, etc. Where were they when the hatch (which was the high level of electromagnetism that Desmond was exposed to) blew up? On the other side of the island! So, they wouldn't have been exposed to that electromagnetism and there for are able to get off the island.
Also, at the end of the Desmond episode, we see Faraday look at his journal and he wrote down something like "if anything happens, desmond is my constant". I think since he was exposed to high levels of radiation during his experiments in the past, when he tries to get back off the island he is expecting to go through the same thing that desmond did. and now that he has met desmond in the past and in the present, then he would be able to have him as a constant, just like penny was desmonds constant.
:X hope that all made sense!