This article in Gizmodo sent me back to my original idea for TimePhiz that I wrote about in 2005 - providing a digital experience in which the backstory is not some mythical fairy tail, but somthing right out of history. I wanted to be able to take a field trip through time. I imagined GoogleEarth with a time slider - and they made that! And when I saw this, well it's like Google StretView with a time slider, too. Unfortunately, you can't download the app in the US - it comes from the Museum of London in the UK.
All I can say is I really hope this catches on. I certainly recognize the value of being able to find a good coffee shop by holding up your iPhone to the street-scape, or even taking yourself on a tour of a new place - but this iPhone app allow you to move the landscape back in time, see people, and get a whole new context.
Of course, this experience is not interactive - those people don't move or talk, but I see no reason why that couldn't happen in another five years.
UPDATE: The app is now available in the US. I've downloaded it, but it's basically just a photo album until you are actually in London (which I'm not).