• by Gavin O'Malley  @mp_gavin, March 2, 2010

Email service provider ExactTarget on Tuesday announced the acquisition of enterprise Twitter management system CoTweet. Terms of the deal were not disclosed.

The deals essentially "bring together all forms of interactive communications," said ExactTarget CEO Scott Dorsey. Founded early last year, San Francisco-based CoTweet has already powered Twitter campaigns for JetBlue, Ford, Microsoft, McDonald's, Sprint, Dell, Pepsi, Whole Foods, Intuit, Salesforce.com, USA Today and Coca-Cola.

The software company's Web-based collaboration platform provides clients with one dashboard for multiple people to track "conversations," assign campaign roles, and create follow-up tasks through workflows and case management. Although it debuted as a free beta, the company began charging $1,500 a month for its services late last year.

Going forward, CoTweet co-founder and chief executive Jesse Engle will continue to lead his team, and report directly to Dorsey.

Dorsey, meanwhile, said he plans to "quickly" invest additional resources to establish the company's Social Media Lab in San Francisco -- "where we'll develop new innovations to help [clients] harness the collective power of CoTweet and ExactTarget to increase customer engagement."

In 2009, the Indianapolis-based ExactTarget raised $140 million in venture capital, and finished the year with more than 30% growth in sales -- which helped it cross a critical $100 million threshold.

In September, ExactTarget bought UK-based Keymail Marketing, which gave the ESP an international reach. Last year, CoTweet raised just over $1 million in funding from Baseline Ventures, Founders Fund, First Round Capital, SV Angel, Maples Investments, and Freestyle Capital.

Despite rumors to the contrary, Twitter is still experiencing significant growth, according to new research from Royal Pingdom, which finds that the microblogging platform is -- as of December -- processing over one billion tweets per month. In particular, January surpassed 1.2 billion, averaging almost 40 million tweets per day. This is significantly more than Twitter was processing just a few months ago.

For Twitter's part, its CEO Evan Williams said on January 12: "Across all metrics that matter, yesterday was Twitter's highest-usage day ever."

In addition, after creating a chart that shows the number of tweets per month back to mid 2008, Royal Pingdom found that not only was 2009 the year that Twitter's popularity really exploded, it also shows that Twitter usage is still increasing rapidly.