“Today is the last day to hit that Stumble button. Thank you to our dear Stumblers for joining us in internet history.“

It’s not quite the end though. All of StumbleUpon’s remaining users will see their accounts migrated to Mix.com, which is a new social sharing platform founded by Camp.
According to Camp, Mix.com will “combine social and semantic personalization into one streamlined experience.” Camp proclaims the new platform will help users find “obscure but interesting content” that has been recommended from within their social networks.
more details on the: Stumble Upon shutdown.