The recently launched Diggbar from digg.com can wrap your site in a frame if the user visits a special URL on digg.com. Your user's experience is negatively impacted:

• the URL in the address bar is 'digg.com'
• your site title could be changed
• content is moved down the page (leaving less 'above the fold')
• it adds visual noise to your site
• it changes your finely crafted visual design
• your site's personality is affected

Many sites (like the NY Times) are, with good reason, blocking this Diggbar. There is a Rails plugin to do this for your site: acts_against_douchebar.