is upgrading Chatter, the Facebook-style social network for businesses that it made fully available in June.

Vice President of Product Marketing Sean Whiteley said Chatter has already become Salesforce’s “most successful product release ever.” More than 20,000 companies are using it. And some of them are buying Chatter on its own, rather than as a free add-on for Salesforce’s sales and customer service tools — for example, Whiteley said Reed Exhibitions has 1,000 Chatter-only users, while Hitachi has 2,000.

One of the big questions around social networking for a company or a team is whether it’s just a toy, or if it actually helps employees get work done. Salesforce surveyed its users, and it says that the average company on Chatter is reporting impressive gains, including a 10 percent increase in productivity, a 25 percent increase in collaboration, and 13 percent decrease in email.

Still, Chatter users have been demanding a bunch of new features, Whiteley said. Salesforce already addressed one of those requests earlier this month with the launch of Chatter mobile apps, but it’s answering even more requests with today’s announcement of Chatter 2, which should be available in October. The new features include a desktop application built using Adobe’s AIR technology, automated suggestions of other employees to follow and groups to find, search capabilities, an email digest of Chatter activity, and more.