The issue is a change in semantics (Score 5, Insightful)

As many readers have commented, this does not seem like such a big deal. Shared stuff being public? Who cares? Don't do it, ya morons! And so on.

I don't use GMail, or Google's reader. However, from TFA and the complaints, it appears as though there was a service where you could aggregate and re-publish feeds through a link that was not (automatically) published anywhere. Google changed the semantics of this, to mean that these "shared" feeds are now automatically available to everyone in your contact list. This (rightfully) has pissed off many existing users, who have invested their time into a system that they must now abandon, because most people have the concept of "mixed company." You don't talk about certain topics in certain groups -- you might be fine making dirty jokes around your regular friends, for example, but you behave yourself when you're at a professional lunch.

So, this is not a matter of not using it -- it's a matter of bait-and-switch. The rules got changed out from under the user's feet, and that leads to a feeling of betrayal in the case where embarrassing information gets leaked. Google gave the impression that you were just hanging out with your friends, and then let in your stuffy colleagues while you were in the middle of telling The Aristocrats Joke.