With regard to the usage of your personal information, just for starters, I agree that we need to define what personal information is. Everyone needs to understand what the rules are and to not have any ambiguity there. So yes, I would say that there need to be clear definitions that everyone plays by. The usage by Amazon is not one of “malintent”; it is to offer a better experience for you, and clearly to not be taken advantage of. Now, that does go up to some interpretation....
I think your other example of posting something on Facebook is a little different, in that you chose to post that. Facebook did not share that on your behalf. You put it up on your Facebook wall. It's clear that you opted in to show this to the world. Getting a few calls from a travel salesman might be the appropriate consequence of oversharing that data, and maybe you won't do it in the future, but that was totally your decision. There wasn't another company making the decision for you.