Nielsen measures interest in categories by the percentage of the web audience that regularly visit such sites. The latest statistics suggest that 65.1% of web users use web e-mail but 66.8% are turning up at social network sites.
This means, said Nielsen, that about one in every 11 minutes a web user is online is spent at one of the sites Nielsen counts in its "Member Communities" category which includes both blogs and social network sites.
Of these sites, Facebook has highest average time per user, found Nielsen.
The researchers also found that social networking sites are managing to reach a very broad swathe of web users. The fastest growing segment of users turning up and using social sites over the last year was among 35-49 year olds.
In particular, the report noted, almost a quarter of Facebook’s users were known to be over 50 years old.