Most servers log every access to the site and my site logs all search requests to my database, I just don't let customers review them is all. I would assume Google has been tracking you all along too, just not in such an organized fashion. Who knows how long Google retains this stuff but my logs are over a year old.
BTW, if I were some people on the net I'd stop running from server to server looking for "nude pre-teens" as that's a common search phrase I see (why? we know why but WHY?) and someone's gonna turn them in eventually.
Overall, having found things on Google I really wanted and then forgot to book mark a site or forgot exactly how I found them the next day when I wanted to look at similar results, this could be a time saving feature.