This feature(?) of IE lets us track the clipboard data using simple JavaScript! You can even post that data to your own server if you want to(this page is not doing that)!
It's a bit scary that a webpage can access/write/delete data from your clipboard.
Below is a simple demo...
Open this page and keep it open. Now, try to go to other applications and start copying stuff to your clipboard. You will see that this page starts displaying that data here!
Here is the JavaScript for this...
window.clipboardData.getData("Text")