Secrets and Lies
In social situations, it is often the ability to keep a secret that determines the course of a social relationship. Secrets are shared as a way of building those relationships, and the ability to maintain shared secrets builds shared trust.
When Google Buzz exposed my list of frequently emailed contacts as a social network, they violated my trust that they could keep a secret.
Abstractly, I think it's a cool idea to build a social network for me, based on data inferred about my communications with Google contacts.
And similarly, I can see how, abstractly, it's a good idea (from a Google perspective) to make your social network public so that other people can more easily, and socially, find people to connect with.
When you combine these ideas, however, you violate the basic social need for secrets to be maintained.
Whether Google is, as some people think, lying, that this was a genuine mistake, or was simply socially inept in combining these ideas doesn't matter.
I expect Google to quietly mine my data and use that to provide me better service (while also making them money of course), but I don't expect them to reveal either accidentally or on purpose anything that I consider to be secret.
People who can't keep secrets aren't usually treated very well by those whose secrets were revealed.

