I had the thought last night that if Google sticks around for the next 50-100 years, and maintains Google Maps, then it could actually turn into a time machine. Load up maps, choose your place and your time, zoom around in street view. I can't imagine how amazing it would be to check out what San Francisco in the late 1960's. Plus, Google will have gathered much more information over the years. They will show photos and YouTube videos taken near that time and location. They might show relevant news stories or tweets they've cached.
Google's stated mission is:
"Organize the world’s information and make it universally accessible and useful."
That's a pretty ambitious statement, but so far it seems like they're achieving that. If they can continue to do it for the long term, they might become the most valuable source of information we have about our recent history. That sounds extreme, but if you take a recent event like the pepper spraying at UC Davis, you can imagine students of the future watching dozens of first-hand accounts from multiple angles on YouTube instead of reading about it in a textbook.
Update: I just found out just after writing this that you can already display historic images on Google Earth, so they're on their way (thanks @ahmattox)