By using either you disclose your network of friends, location, the content of your communication, and -- if you didn't take steps to counter it, essentially the majority of web pages you visit.
Well, to some extent they could get a good deal of this information from being in bed with the phone company and the mail service. The difference nowadays is that making things digital has drastically reduced the cost of operating a surveillance dragnet (e.g. cost of copying / storage).
Facebook has web bugs on a significant percentage of web pages, perhaps the majority by visits. They have, in effect, recruited the entire web to spy on users. For reference, the Stasi had at some point 30% of citizens filing surveillance reports on the lives of others.
All voluntarily. Stasi would be jealous.