My co-author on Expert F#, Adam Granicz, has been leading Intellifactory to develop the F#-based WebSharper platform for developing client-server applications that execute as Javascript in the browser and as compiled .NET code on the server. 

Intellifactory seem to have set about answering the question of "just how simple, clean and productive can you make developing rich web applications that target Javascript?" (my words, not theirs).  While still in beta, signs are that Intellifactory are putting together an impressive technology that makes really good use of F#'s unique facilities to simplify this class of applications. WebSharper seems to draw inspiration from LINKS and Tomas Petricek's AFAX project, with an added focus on simplicity and productivity.

Anton has a good introductory blog on developing with WebSharper here.

We also owe a huge thank you to Intellifactory (particularly Adam and Anton) for their excellent, timely high quality feedback on F# itself.

Here's an excerpt from the Intellifactory website:

The IntelliFactory WebSharper™ Platform

Writing good web applications is not an easy task today. It requires a mastery of numerous languages (JavaScript, HTML, CSS), and an acute awareness of existing standards and browser implementation quirks. Poor debugging tools, and the lack of compositionality and component reuse in the multi-tiered, multi-language web environment compound the problem even more.

With the IntelliFactory WebSharper™ Platform you can develop rich, client-based, and highly responsive web applications using F#, enjoying all the benefits of Visual Studio™ and IntelliSense™. Developing both the client and server-side functionality with F# gives you unrivaled productivity, a dramatically more compact code base, and powerful language features to get your tasks done quicker, more robustly than ever before.