Google Reader is Google's feed reader, and its users can choose to share items that they read. The sharing is/was done by clicking "Share" on relevant items in your feeds, and you could give other people a unique URL (containing random looking characters, possibly just an obfuscation of your username, who knows) and they could check your shared items or even subscribe to them.
People used it for all kinds of things - political news pieces for likeminded friends, some spouses shared raunchy things, some dude even made it part of his business.
One day Google decided that all of your friends should be able to see your shared items. And that your friends are everyone you've ever sent email to from your gmail account. This caused a bit of anguish for a fair few people - family rifts, job issues, etc...
The official workaround was to either unshare the items or delete people from your contacts list. Sometime after that they added the ability to not have everyone you've every contacted be your friend, and now I believe there's an option to opt-in to the feature and then select who gets to see it.
No trace of an apology to anyone, and the thread of angry people in the reader google group basically got admonished for believing that the pseudorandom looking URL that only the user had access to in anyway implied that the data was private. If the shared page was www.google.com/readers/[username] that'd be fair enough I guess.
For some people it was as big a deal as making everyones email readable by any and all, and there wasn't any kind of official response that acknowledged it was a misstep, let alone apologizing.
I figured since it was around a month after the Beacon fiasco at Facebook that they'd decided that an apology would get them bad PR and so they just ignored the upset people. I switched to Bloglines, and I imagine quite a few of the people who were effected by or noticed what happened did as well.
That said, I'm significantly less comfortable with Facebook.