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Clearspring (news, site), best known for its "AddThis" widgets for making it easier for readers to forward links to a page to their social media community, has raised an additional US$ 20 million, now from Silicon Valley investors -- and hinted that it might go public.

New Investor Funded Twitter, Zynga

Clearspring Technologies, founded in 2004 in McLean, Va., had a bit of a rocky time in 2009, as did we all, but its 2008 acquisition of AddThis has apparently saved the day. The company announced that it had closed a US$ 20M fourth round of funding led by Institutional Venture Partners (IVP).

IVP, a Silicon Valley-based later-stage venture capital and growth equity firms, has funded such household names as Twitter and Zynga. This is in addition to Clearspring's existing investors New Enterprise Associates, Novak Biddle Venture Partners, former AOL vice chair and president Ted Leonsis, AOL co-founder Steve Case, Capital One co-founder Nigel Morris and Silicon Valley super-angel Ron Conway.

But it could mean more. As Hooman Radfar, co-founder and CEO of Clearspring, notes in a blog post, "86 out of the 300 companies they last invested in have gone public." And the company recently added Bill Wise to its board of directors -- associated with DoubleClick's IPO, MaxOnline's sale to Excite and Right Media's sale to Yahoo.

Is this a hint? Are we back to the 90s again?

Little Widget That Could

You've seen AddThis, even if you didn't know it. It looks like this:

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And it's become the go-to guy for building web engagement by making it easier for Web users to propagate content to their social media networks. According to Clearspring, AddThis is now used by more than 9 million domains, links to more than 300 social networks and reaches more than 1 billion unique users monthly. The company says it's now processing 10 terabytes of data per day -- which it says is as much as the entire digital Library of Congress every week. 

What that means, of course, is that Clearspring can deliver more to advertisers -- not the least of which are up to 172 million Twitter and Facebook users.

According to the company, the funding will be used to accelerate Clearspring's next-generation publisher products and continued growth of its advertising offerings, as well as to help fuel strategic acquisitions -- you know, like AddThis was.