The most recent numbers from Nielsen show that we are spending more time social networking than ever. As of May, Facebook was still number one. And Twitter continues to grow - though it is showing some signs of slowing down.

How about some numbers?

• Facebook had 144.3 million unique visitors in May, making it the world’s top social network for the seventh month in a row.
• Former top site Myspace.com was the top social network when ranked by total video streams, with 116.1 million.
• Upstart Twitter was the fastest growing site in May, increasing a mind-boggling 1,448 percent year-over-year.

Of course, it’s easy to post huge percentage gains when you start from a relatively small number. The site had 18.2 million unique visitors last month (slightly more than 10 percent of Facebook’s total). During the same month a year ago, Twitter had 1.2 million visitors.

It’ll be interesting to see if Twitter can keep up this rate of growth. ReadWriteWeb points out that Twitter’s month-to-month growth seems to be slowing down.

It is important to note, though, that Twitter’s growth has slowed down dramatically over the last two months, as both the time per person spent on the site and Twitter’s month-over-month growth only increased slightly since April 2009.