Despite the fact that it's opt-in and has decent privacy settings, I find Google Latitude's location history dashboard a bit creepy. It now gives step-by-step views of where I've been and even knows how many total miles I've traveled.
I will admit that the little feature that explains how many miles one has traveled in terms of distance from the moon is neat though:
You can enable location history in your Latitude settings, but keep in mind that this is still an experimental feature and not entirely flawless. [TechCrunch]