Google has launched a new way for sites to opt out of having their content show up in Google Shopping, Advisor, Flights, Hotels, and Google+ Local search.
Matt Cutts announced the feature in a very brief post on the Google Webmaster Central blog, saying, "Webmasters can now choose this option through our Webmaster Tools, and crawled content currently being displayed on Shopping, Advisor, Flights, Hotels, or Google+ Local search pages will be removed within 30 days."
This is obviously not a feature that Google would want a ton of people to use, because the less content that appears in these services, the less useful they are. Perhaps that's why Cutts hasn't tweeted about the tool (maybe not, but perhaps). At least with the short announcement, they have something they can point to.
The feature is a direct response to an investigation by the Federal Trade Commission. When Google settled with the FTC, one of the voluntary concessions Google made was a feature that would let sites opt out of Google's specialized search engines.
As Danny Sullivan notes, the feature doesn't let you choose which search engines you wish to opt out of. If you use the feature, you're opting out of all of those mentioned.
On a help page, Google says, "This opt-out option currently applies only to services hosted on google.com and won't apply to other Google domains."