I don't remeber the exact site I was on, but there was an option to find "your location" - your actual physical location. I kinda thought there was no way this could be done as best anyone should be able to do would be to query your device's IP address and make an approximate guess down to a city or suburb level.
I was wrong: The site returned my physical location within 50m. This was a concern since this info was collected without my knowledge and permission.
So how was this done?
If you recall, when the Google streetview car drove thru the streets taking photos it also scanned for wireless network access points and captured the IP address, plus a vast array of other data including your internet traffic if your access point wasn't secured (I believe there's legal action in Europe on this issue).
This infomation is in a DB and can be used to query your physical location. Ideal for advertising since your location info can be tuned to suit your locality - this may be ok for many surfers.
However, firefox has location info that it passes to google and is switched on by default. I was kinda surprised at this. To view your settings in firefox:
In your address bar type: about:config
Accept the warning. Then in the filter search type: geo
You'll see two values: geo.enbled and geo.wifi.uri
Both with have values and one will point to a google url.
You can double click on these values to change them. eg turn geo.enabled to false and geo.wifi.uri to an empty value.
There's probably a host of other methods that are being used to capture location and other info as well. eg like a website being able to remotely collect the clipboard data from internet explorer - fixed in the latest versions.
Corporations are using technology and good ideas to drive profits.