@Helter:
I know this is the Dumb Predictions thread, but it would be really cool if the reason why Brook decided to stop being a knight (or something like that) to become a pirate had something to do with the Vinsmokes.
This part of my prediction seems indeed plausible. Brook has obviously some knowledge about the Vinsmoke's and my bet is it has something to do with his past.
I though about something else also. Laffite sword look almost the same as Brook one. I don't remember from what sea Brook and Laffite are from but if they where from the same, they could have learn the same fighting style. That would be cool. But I remember hearing that Brook has developped is current style based on his body. I don't know.