Google  expanded Latitude yesterday to include Location History , a new view that essentially traces your steps via your smartphone. Where was that cool path through the park you found a few weeks ago? Latitude knows.
The new History Dashboard remembers everywhere you've been, and actually uses that information to provide even more information. So it'll tell you not just where you've been, but provide information on that subject--want to know the history of that path? Sights along it? Other entrances? Weather forecasts? It'll link you to all of that stuff. That's in addition to some of the more baseline data like how far you've traveled in any given amount of time (and, in a cute twist, what percentage of the distance to the moon you've traveled).
History Dashboard, like Latitude in general, is an opt-in service. That's a must, because it's inherently very creepy, even if you want it. So you have to sign up for it, at which point Google flashes a big warning saying "THIS IS SUPER CREEPY DUDE ARE YOU SURE YOU WANT TO DO THIS," at which point you hesitate and maybe move to a cabin in the woods. Thoreau never dealt with this stuff, you know? If you do decide to take the plunge, you can erase any and all location history. But be careful: I erased all the time I spend on my couch, and Google tells me I no longer exist.
The History Dashboard is available now from Google's site.