Brits love YouTube, according to new figures from analysts Nielsen Online.
The video sharing site has knocked Wikipedia off its top spot on the UK hit-list, winning 10.4m visitors in January alone.
This is a 56% increase in traffic from January the previous year.
Wikipedia, which had previously been rated number one, had 9.6 million unique UK visitors, while Facebook had 8.5 million people visit it.
Blogger, the DIY blogging service also owned by Google, had 5.1 million users, ahead of MySpace at 5.02 million and Bebo at 4.09 million users.
Nielsen Online estimates that nearly two-thirds of UK web users - or 20.8 million people - visited at least one of the top 10 social networking sites.
The biggest growth was seen by Facebook, despite rumours of a slowdown, which enjoyed a 712% boom since January 2007.
Also gaining fans is the photo website, Slide, which saw its user base increase by 207% to 3.3 million over the same period.
"The fact that almost two-thirds of Britons online visited at least one of the top social media sites shows it isn't a niche part of the internet but is now the backbone supporting its growth", Alex Burmaster, Nielsen Online's web analyst told The Guardian.
"Whilst the majority of the most popular social media sites are the networks, most of the fastest growing are video sites, which points to video being the biggest star of the 2008 social media scene."