Just read an article over at harriyott.com: Looks like there are JavaScript functions built into IE that not only allow a site to set the contents of your clipboard but retrieve them as well.

IE users, try this one on for size (this only works with Internet Explorer, to my knowledge):

First, click this link to copy the phrase "My Dog Has Fleas" to your clipboard. Now open up a Notepad window (or whatever your favorite text editor is) and paste it in - sure enough, it adds info to your clipboard.

Now copy some arbitrary text to your clipboard. Doesn't matter what it is - type something in that Notepad window, or highlight something on this page, and copy it. Now click this link to show your clipboard contents.

Pretty freaky, huh?

For the curious... the "insert data into clipboard" code is:
window.clipboardData.setData('Text', 'My Dog Has Fleas');

...and the "retrieve data from clipboard" code is:
window.clipboardData.getData('Text');