Just a week and a half after Facebook surpassed the 110 million active users number, the company has surpassed 120 million active users according to the site statistics. Additionally, Sheryl Sandberg mentioned the number in a press release announcing the integration of Force.com and Facebook. Sanberg said, “Our work with salesforce.com will give developers the tools to create and deliver a new class of business applications for Facebook’s 120 million active users.”

More on the Salesforce partnership to come. This is rapid growth for Facebook and it suggests that the company may be growing at a rate faster than the 250,000 daily users rate previously mentioned by Facebook. While numbers provided by Facebook vary and are not exact, the company is on track to potentially surpass 200 million active users by the end of the year.

While many have criticized Mark Zuckerberg for not focusing on the monetization side of the business yet, providing a scalable infrastructure that could theoretically surpass half a billion users in a little over a year is a complex task. While there is no doubt that the company will continue to grow at a rapid pace, you have to wonder how long the company can continue to grow at this pace.

If international growth rates are any sign of how long this could last, Facebook could soon run up against some hurdles. While growth rates in South America and a few other countries around the world have been phenomenal, there have been serious challenges in Asia and parts of Europe where local social networks continue to dominate.

The growth isn’t ending for now though. As we wrote this morning, the company has become more popular than the BBC. We will continue to monitor as it grows internationally.