Facebook has moved one step closer to becoming the largest U.S. social network according to the latest data from Compete.com. Data from October shows that Facebook grew domestically by almost 4 million while MySpace continued their monthly decline, shedding over 1.58 million users, despite the launch of their highly buzzed MySpace Music product.

It’s clear that in the U.S. users are shifting from MySpace to Facebook and there are no signs that the trend is stopping anytime soon. Facebook also continues to experience massive growth abroad with more than 120 million active users. At Web 2.0 Summit today in San Francisco, Mark Zuckerberg suggested that around 50 percent of users return to the site daily.

I’m not sure if he misstated that metric but it’s clear that the site is highly addictive and enjoys a rapidly growing user base. While the latest data wasn’t that surprising, the company had a flat month previously suggesting that their domestic growth might begin to slow. For now there is no slowing and the site continues to surge.

We’ll continue to monitor both domestic and international growth as Facebook expands. At this rate, Facebook could potentially surpass MySpace by the end of the year.