I recently found out that in Internet Explorer (v9 at least), the "Pin it" button for Pinterest is breaking 'back' functionality in the browser. Right-clicking on it shows an entry like 'http://assets.pinterest.com/pidget.html' as the previous page.
Looks like Pinterest is adding an iFrame and IE is adding its address to the history. Clicking 'back' doesn't do anything. Is this a known issue and is there a fix for this?