A couple of days ago I mentioned some Greasemonkey scripts I wrote. One of them, which I didn't discuss, is particularly devious.

What happens when users have the ability to hijack sites and how they expect to be used? For example, there are scripts to provide mapping functionality within Flickr!, or to compare book prices on Amazon.com with other vendors.

MapThis! overrides the "Map This!" link that shows up in GMail when an address is detected. Instead of linking to just a plain-ol' googlemap, the link is "hijacked" to provide routing directions from the user's geolocated position (using HostIP) to the address in the email.

This is useful, for example, if a friend sends you the address of their house, or that cool roller-rink with disco ball that you're meeting up at and you want to quickly get directions.

It also demonstrates how a user isn't limited by the interface a site-designer supplied, allowing them to customize and use the site as they wan.