According to new data published by Nielsen Online yesterday, Facebook is currently the largest social networking site in the United States based on the amount of time spent online. Over the past year, the time spent on Facebook has increased 700 percent in contrast to MySpace, Facebook’s largest competitor, where total time spent has decreased 31 percent. Not surprisingly, Twitter managed to post impressive growth of 3,712 percent.

Twitter still represents a serious threat to Facebook but the company (Facebook) continues to post impressive growth statistics despite the presence of significant competitors. Yesterday there was also a bit of a debate over Facebook’s video service versus MySpace’s video service which currently holds the title for most streams over the past year. Some were arguing that total number of plays is not an accurate measurement since Facebook’s video service is used for sharing personal videos, not general media.

It’s a valid point but ultimately I don’t think comparing the two video services is really the best metric. Ultimately Facebook continues to expand rapidly, attracting millions of new users a week, and many of those users continue to be engaged. So how does Facebook continue to sustain such incredible growth even as the largest social platform even? No other social platform (or social network) has ever succeeded at sustaining growth beyond 225 million users.

Facebook invests a large amount of their resources in monitoring internal metrics. Facebook has continued to do so with the latest design to ensure that users don’t end up leaving the site. As the company tries to simplify the user experience and expand beyond their current size, it’s clear that their internal metrics appear to be doing the job. It will be interesting to see how long Facebook can continue to grow.