Google has sent ripples of horror through email privacy activists, concerned that the company's decision to include messages in regular search results could lead to embarrassing previews during public browsing. Currently an opt-in system, the Gmail Search Field Trial promises to include relevant emails in among search results, including contacts and shared links; however, there are also safeguards in place just in case you don't want whoever is standing over your shoulder to see what mailing lists you're secretly signed up to.
The Gmail section will in fact be split off, to the side of the search results, rather than integrated in-among them. That box will also be hidden, opened up with a click according to Robert Scoble, so that messages won't be visible unless the user chooses to have them be.
Email will of course only be shown to the individual user - the data in your messages won't be used for other peoples' search results - and the indexing itself has already taken place as part of Gmail's own search system. Nonetheless, Google is being tentative in how it rolls out the system; membership in the field trial is expected to be strictly limited, and initially only available to uses of Google.com.
The new system is part of a range of updated search options Google has announced recently. Most obvious will be the Knowledge Graph, a carousel of results with contextual links and other information, based on the assumption that the user is likely to want to know more about the topic.
Meanwhile, Google also promised Google Now style voice search functionality for iOS users, though the contextual part of Google Now will be kept to Android devices for the moment.