In the company’s blog post it has been said,

After nearly two years as a subsidiary of eBay, today StumbleUpon returns to being an independent company.   StumbleUpon is now backed by myself and co-founder Geoff Smith, along with several great investors who’ve backed companies such as Google and Facebook.

StumbleUpon had hit 7 million registered users last year, which was at the time 50% higher than the number of Twitter's users. Twitter's users have dramatically increased this year though.

Both Twitter and StumbleUpon, though, are tools of discovery, sharing and social connection. They are different in some ways but similar in others. There's a special kind of magic to StumbleUpon, though, and we're very glad to see its founders back in the driver's seat. A web where Twitter and Facebook are the only social discovery games in town is a poorer web.

In the company’s blog post it is further said that:

This change will help StumbleUpon move quickly and stay true to its focus - helping people discover interesting web content.  Our goal is to make StumbleUpon the web’s largest recommendation engine and we think this is the best way to get us there.
Thanks to everyone for helping make this happen. While there will be some internal changes at SU, it will not impact the Stumbling experience and will help us create the best possible product.  We are really excited about this change, and hope you are as well.

Lets see if the original founders of StumbleUpon will take it to the new heights.