Re: "people already hand over masses of info to private firms"...
> I rather fear that the reality is that you have handed over more data than you think.
The wise position for any privacy-conscious person to take is to assume that that is in fact true. They've already collected unknown data, so be aware that anything you let slip - however innocuous - could be used in combination with that unknown data.
For me, it's basically the same mindset as when dealing with security systems. It's not IF there's a breach, it's WHEN.