Lost in the news bite about Google adding two-factor authentication was the statistic that Google Apps now has 3 million business customers of various sizes.

Google Enterprise President Dave Girouard made the announcement in a blog post Sept. 20 time for the Google Atmosphere cloud computing event in Paris. Girouard wrote:

"As of today, more than 3 million businesses have gone Google, and over 30 million users within businesses, schools and organizations now depend on our messaging and collaboration tools."

Congrats Google, but far from relaxing, you must land more, larger customers before Microsoft and IBM grab them.

While I've watched the Google Apps team add Google Sites Website publishing functionality, the less-than-popular Google video for businesses, rewriting Google Docs and several other features, it's been the growth in customers that I've been most interested in, starting with the Capgemini win back in September 2007.

Google hit the 2 million business customers 11 months ago, announcing the milestone in conjunction with the worldwide expansion of its Going Google ad campaign.

Key Google Apps customers include Motorola's handset division, which has 20,000 users. And Konica Minolta has 7,000 workers who have gone Google. Business services concern Rentokil Initial moved its 35,000 users to Google Apps.

Moreover, Google landed entire educational institutions for Maryland, Oregon, Colorado and Iowa, and municipalities such as Los Angeles, for whom it replaced Novell and beat out Microsoft and its competitive Business Productivity Online Suite.

Google is also one of the frontrunners to win the 15,000 seat General Services Administration collaboration contract after earning FISMA certification, a stuffy security protocol the GSA requires.

But, and this is a big but, 3 million business customers is a drop in the bucket versus Microsoft's massive Office and SharePoint install base of hundreds of millions of users. And 30 million users for Google Apps is a fraction of the 150 million legacy IBM Lotus Notes users.

And with Microsoft BPOS and then IBM LotusLive Notes now providing strong cloud computing offerings, I'd be surprised if Google makes it to 4 million business customers by this time next year.

I expect Google Apps growth to slow a bit as the competition in the cloud thickens, but wouldn't it be cool if Google proved me wrong this time next year?

Wouldn't it even be better if the company landed a Coke or some other massive multinational company?

Update, Sept. 21: Microsoft Senior Product Manager Andrew Kisslo had his own comments about Google Apps and its momentum.