We hear that the paperwork has just been signed on a monster new funding round for Yammer. There was more than $100 million in interest, and the company took just north of $50 million, last we heard, although that  may still creep up as the deal closes.

The earlier reports of fundraising may have been premature, because our source very close to the deal tells us it came together in a rapid 48 hours. It’s hard to believe the company has kept a lid on the news since January.

Yammer Founder and CEO David Sacks declined to comment.

Yammer has nearly 200,000 business networks on its site, and although we weren’t able to confirm the revenue numbers, the company recently hired David Obrand, the former VP of sales for Salesforce. People like that don’t usually join a company unless revenue is starting to seriously hockey-stick. Sacks has said in several previous interviews that revenue tripled last year.

Separately, Yammer competitor Jive reported its first quarter as a public company today and revenues were up more than 50%.

We weren’t able to confirm Yammer’s valuation, but I would be surprised if Yammer weren’t nearing the $1 billion valuation club that so many other hot enterprise companies are now members of. [UPDATE:  A source who looked at the deal early-on says the valuation was closer to the $500 million-range. We're still not sure where it ended up.]

As a side user note, Yammer is sticky as hell. After using (and sometimes complaining about) it at TechCrunch, I lasted about two weeks running a new company before we installed it and made it mandatory.