Now, that's only one bit of data but if you want to be sure you can set up a trigger page of your own.
The way it works is simple, I made a random url, stuck a script in there that sends an email with the url as the subject header. The first script I visited using chrome, the second script I mailed myself a link to from another email account to a gmail account. Both scripts fired when chrome activated the links so I know they work, then I simply let it rest.
I guess the gmail one would require re-crawling of all gmail for it to fire, the chrome only one would be dependent on the version of chrome that I ran the test on phoning home with the link, and I did not re-try this for every version of chrome (or on every platform). So it's not a perfect method but it definitely puts the lie to chrome or gmail data being directly used to power google search results that people would expect to remain confidential because only they have the urls. Score one for obscurity and nice of google to ignore these paths.
I could set up another url for a test using the DNS but you're free to do so yourself as well of course, it is definitely an interesting idea.
And if either of those scripts ever does fire I'll rip google a new one, that would be the sort of abuse of trust that gets my temperature up. But for now I'll take the fact that it hasn't happened as proof that google can be trusted with data to some extent.
This includes navigating the URL structure (in finding blah.com/one/two/three.html there may be attempts to /one/two and /one) and password-protected admins which are not linked to from anywhere (we suspect Analytics or toolbars are telling Google these pages exist). As a result, Googlebot generates a bunch of false positives in our error logs.
Though I don't think it's happening, I've thought it'd be very clever if users became the search spider for Google, telling them when content had gone stale and/or doing the spidering on Google's part. Just by using Google's browser.