I think there are lots of us out there who have left a voice mail at one time or another and wished after we left it that we hadn't said something in the message. At least we can typically rest assured knowing that only the person we sent the message too would get it. If you use Google Voice, your voice mails may have been indexed and offered up in public search results.
Engadget reports that at least some of the voicemails left on Google Voice accounts have turned up in the search results. You reportedly have to type in a special search query "site:https://www.google.com/voice/fm/*" and get a few pages of returns. It appears that most of the returns are gibberish test messaged left by early users or testers of the service.
However, a few of the messages in the results appear to be from users that would no doubt be angered to find what they thought were private messages online for all to see. As of now, the only official word from Google is that it has changed how shared messages are indexed and made available to the public. Presumably that change will prevent this from happening again.