Although Yammer and Salesforce have had a bit of a rocky past, Yammer recently announced that it was integrating activity streams from Salesforce into its own service. This means that sales leads, marketing campaigns, and other content that is entered into Salesforce will appear in Yammer’s stream as well.

The announcement was a bit surprising especially since it was just earlier this year that Yammer CEO David Sacks slammed Salesforce over its new social service Chatter. He told Chris Crum of WebProNews:

“Chatter is Yammer circa 2009,” he said. “There are no features we didn’t have two years ago. Obviously we’re on to Yammer 2011, so they’re pretty far behind. From an innovation standpoint, the launch of Chatter.com is a total non-event.”

Here is a video account that further details the history between the two companies:

However, as Sacks explained to us just recently, Yammer released its activity stream API not long ago in order for other enterprise applications to be able to push their stories into Yammer’s stream. In other words, as long as another company has an accessible API, Yammer can integrate their activity into its feeds without a formal partnership between the companies taking place.

He told us that the integration with Salesforce happened this way and that it allows the activity stream to be socialized and shared with more of the company.

“By pushing these activity streams into Yammer, these stories can now be shared with a much wider range of employees,” said Sacks. “It can, basically, be shared across the whole company.”

He refers to Yammer as a “private enterprise version of Facebook or Twitter” and said that the company’s goal was to “bring into Yammer all the conversations that are relevant to employees of the company.” Because social networking is one of the most efficient forms of communication today, he believes that enterprise applications should encourage socialization and sharing throughout the entire company. If not, the company will become siloed with each department dependent upon its own social network.

“You still need, we think, a social layer across all these applications where we can aggregate these feeds,” said Sacks.

Yammer is striving to become this “social layer” and believes that this integration will help it meet this goal.

In an effort to let people know about this integration, and its integration with NetSuite, the company launched a “Friends with Benefits” campaign, coincidentally during Salesforce’s Dreamforce event. The company went all out for the event and even had a Yammer mascot holding hands with the Salesforce mascot promoting its free Starbucks drink.

“Certainly, Salesforce is a very special friend with benefits, but it’s not our only friend with benefits,” said Sacks.

He also told us that Yammer hopes to work with more enterprise applications in the future.