Update: the site has now launched officially at iphone.facebook.com

A reader tipped us off today that Facebook has launched a version of the site for the iPhone. And - wow! - have they done a spectacular job with this.

Go to themob.facebook.com on your iPhone or web browser to behold what might be the best iPhone app so far. The interface slides horizontally as you choose options, and the site is laid out in such a way that the essential features are much easier to find than on the main site - browse friends, check your Facebook mail, read the news feed and use pretty much every other Facebook feature from this more compact viewpoint. The red number is your unread mail: my inbox is unusually empty at 35 mails, but I guess that's no consolation for those who tried to contact me through the site.

This is a good job by Facebook, and hopefully other social networks will launch iPhone versions that are even half as good.