it sounds like its adding a messaging system that will need information other than transfers of funds to be passed.
Not necessarily a bad thing, it depends what the message is!
SatoshiDice is the classic example. They were using lots of single Satoshi transactions as a way of proving the validity of their bets. Blockchain space got gobbled, Bitcoin devs had to contemplate how to dissuade them from doing this. They weren't sending money for the purpose of someone else receiving that money, they were doing it as a way to send a message that had the effect of providing evidence of the trustworthiness of their betting system.
Payments Protocol solves this problem, but also gives the person who draws up the payments request the option to have the message authenticated by a CA. This is where your own personal details might get associated with the public key you use to pay that person. In a webshop -> customer transaction, the webshop might include the product, and a confirmation of the Name & Address to deliver to. The information in the message is all under their control, and we now know this can be slurped by the CA, and in turn by our friends at the NSA.
There's no reason to assume the payment requester to disclose details that identify either you or your purchase items in the Payments Protocol message, this is not mandatory to the protocol (I hope!). Although, the merchant requesting payment should choose something useful to the user, and relevant to the transaction. Imagine buying from a webshop, confirming the order, being presented with a payment request message triggered in your Bitcoin client, and the message being completely or nearly blank! It would seem a little strange, you'd wonder if the Payment had been successfully attacked and you were sending your money to an attackers address (the attacker's method maybe didn't or couldn't copy the message into their spoof message).
And so there lies the rub, you can kind of assume that the more correct information about the transaction that the merchant includes, the more convinced the end user will be that they're accepting a request to pay from who it's supposed to be from. And hence the more information for the NSA to slurp.