Latest Nielsen Online survey reveals Facebook as clear leader in social networking sites.

With a year-over-year growth of 3,712% for minutes spent on site (299,836,000 in April 2009 compared to 7,865,000 in April 2008), Twitter is hardly an insignificant social network. However, according to a recent Nielsen Online survey, it is still only the fifth most used network behind Tagged.com, Blogger, Myspace.com, and industry leader Facebook.

This is good news for Facebook whose worth has recently been valued at $10 billon and has held the lead in both time spent on site and unique visitors for the past four months. Additionally, its 700% year-over-year growth in usage (13,872,640,000 in April 2009 compared to 1,735,698,000 in April 2008), while nowhere near Twitter’s growth, is well above the industry average of 83%.

Former social networking leader MySpace, while still ranked second, has seen a 31% decline from last year in time spent on page (4,973,919,000 in April 2009 compared to 7,254,645,000 in April 2008).

View the full details of the Neilson Online survey here.