As expected, Google has officially announced the spread of its +1 button for websites, marking the company's increasing challenge to Facebook sharing. Just as it already does in search, allowing users to recommend links to their friends, +1 for websites will allow readers to flag up interesting content that will be promoted in the future search results of their contacts.
As well as third-party sites rolling out the button today, +1 will also be showing up at YouTube, the Android Market, Blogger and in Google's Product Search. You'll obviously need to be signed into your Google account - and have some linked friends - in order to see their recommendations.
There's information on implementing +1 on your site here, though right now the results are only showing up on English-language Google.com searches. Still, with Google chairman Eric Schmidt admitting the company was slow off the mark to address social, it seems likely it will push ahead strong on the +1 roll-out.