I recently encountered two unexpected examples of location-based services that show how useful it can be if a service provider knows where you are when accessing his service (even though the whole concept has its scary aspects as well).

I am using a commercial VPN service (5 USD/month) now to jump over (or dig through) the Great Firewall, and as a side effect this makes my Internet access appear to be originating from the US or Europe. Now Google showed me a warning message about my account being accessed from an unlikely location, and advised my to change my password if I had nothing to do with this. Apparently, they keep track of your physical location (which can be determined relatively accurately from your IP address, unless you are using something like a VPN or proxy server) and if your point of access moves faster than a human being could, they generate the warning.

And yesterday, my sister and I received text messages to our mobile phones with Expo information shortly after we entered the Expo site. Your mobile phone operator obviously knows where you are (in urban areas within a few hundred meters), and they can use this information themselves or share it with partners to provide location-specific information.

The scary part is the ability to record and store this data, combine it with data from other sources to get an uncomfortably comprehensive profile, and share it with people you would rather not disclose your location to. But it sure is pretty darn useful.