Last month Compete published a re-arranged list of the top 25 social networks:
As expected, Facebook finally over passed Myspace. On the other hand, Twitter is quickly going up, last year it was at position 22 and today is at 3!
It is also interesting to see the details on the time spent by users. Last month Facebook users spent 16.41 minutes in average per visit, while Myspace and Twitter users spent around 9 minutes.
More info at Compete.