@Deicide:
Hey, the thought just came to me: does Brook even know about the Pirate King Gol D. Roger?
Well I'm pretty sure we'll get an idea about what Brook may know whenever he starts talking with the rest of the Strawhats. The others might mention a name and Brook will interject with something that only someone from his time may know about.
Brook has been in the Florian Triangle for 50 years in a ship with a broken rudder. He has met people very rarely, and often people would shun him away, attack him or ignore him because he was "just dead bones". Would he heard of the exploits of the Pirate King, of the White Beard or other world powers there?
Likely he's heard of people like Whitebeard, Garp and Aokiji since they've been around in the One Piece world for a long time. If he knows about others such as Shanks, Mihawk will depend if he ever got information from ships coming into the Florian Triangle. I highly doubt it since during their first meeting Brook was so ecstatic about the crew not running away from him in fear.
Maybe he does know a little (he knew what was a Shichibukai, after all), but I wonder if he can give us a fresh perspective of how the world was before the rise and fall of the Pirate King and the coming of the age of pirates. Was the New World ruled by emperors back then? Was Whitebeard an emperor already? Who were the emperors then? Did the idea of the Shichibulai existed?
That's the way I see it as well. Brook can be the the one who knows of how things actually worked back before Roger's speech caused the influx of pirates. We might get a view of how different things are running now from back then. Since I personally think there weren't nearly as many pirates during Brook's first life as a pirate compared to now.
I believe the three world powers system already existed back then, and Roger was so fearsome because he in effect almost defeated the three world powers. However, at least two Shichibukai (Croc and Moria) wanted to become the next Pirate King before their dreams were crushed and they were conscripted into the Shichibukai, so at least two of them are younger than Brook's time. The others we know to not seem to have more than three decades of life.
I actually think only two of the three world powers were around. The Shichibukai I believe were a recent addition to deal with the rise in piracy since Roger's death as I mentioned above. During Brook's time I doubt there were really alot of crews that were considered threats to the World Government compared to now. So you have someone like Whitebeard who's been around for awhile on the pirates' side, people like Aokiji and Garp on the Marines' side.
Then when you have a wild card like Roger showing up and shaking the foundation as much as he did, you'd want to to take precautions to make sure something like that doesn't happen again. Now you have people like Luffy and Blackbeard who aren't answering to anyone, who like Roger, are wild cards in this whole thing that risk causing such a stir to the status quo. Luffy is more open about it as we've seen, but Blackbeard is just now making his move to become Pirate King.
So I think after pirates starting popping up from everywhere, they started the Shichibukai to avoid spreading themselves to thin. What better way to at least attempt slowing down piracy then finding already well-known strong pirates, recruiting them to your side to instill fear in lesser known crews and people even thinking about becoming pirates. So I'm guessing it was alot easier as a pirate back in Brook's voyage with the Rumba Pirates then it's going to be now.