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This is bound to be an anti-climax after news that eBay may be acquiring them, but StumbleUpon will announce on Friday the launch of StumbleThru, a "a new way to explore personalized content within fast-growing sites such as Flickr, MySpace, Wikipedia, and YouTube." No mention of eBay, though!
It's basically a domain-specific StumbleUpon that lets you focus on your favorite sites, rather than stumbling more broadly. So if you're crazy about Flickr photos, just Stumble Flickr. The full list of supported sites is: Flickr, MySpace, Wikipedia, YouTube, BBC, CNN and Physorg. When the service is live, it'll be available at stumbleupon.com/stumblethru
See also StumbleVideo, another recent launch.
Update: More coverage.