But more seriously it really depends on what appears in that search results and for which queries. If it's done properly it only triggers when there's a very relevant mail matching the query, which would be unlikely from just a casual search from a friend.
Also if just the title is shown, it doesn't reveal much.
Yeah, I don't want to imagine what sort of search your friend would be doing on your computer that would bring up your porn subscription, your emails to your mistress...
But more seriously it really depends on what appears in that search results and for which queries. If it's done properly it only triggers when there's a very relevant mail matching the query, which would be unlikely from just a casual search from a friend. Also if just the title is shown, it doesn't reveal much.