StumbleUpon has recently undergone a massive re-design of their core site. Of all the significant changes, one stands out above the rest. The social site removed direct website links, and instead uses iFrames to display the stumbled site.
In addition to the iFraming of all external site content when logged into the site, StumbleUpon doesn't offer a way to remove the iFrame. For users not logged in, StumbleUpon offers a clickable X button to escape the experience. These recent changes may impact the positive SEO value that the social bookmarking site has on marketing campaigns.
Perhaps, users may grow concerned over time with these changes. It strikes us as slightly annoying.
