Last week, Katie lamented the lack of an iPhone-specific Facebook version, but we had heard that one was coming... and soon. Mashable spotted the test version of Facebook's iPhone which had been housed at themob.facebook.com but quickly removed.
According to Mashable this "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.
Of particular interest, Joe Hewitt replied in the comments indicating that he was responsible for the iPhone implementation of Facebook and that the official launch is coming soon. Hewitt is responsible for much of the early javascript/web implementations for the iPhone (Wired profile)
So hang on Katie... it'll be here soon.