This is a pretty late reply, but so far my experience is that as a language, F# can be applied to just about any problem.  It seems to lend itself to expression of algorithms, language and data structure parsing and manipulation, implementation of complex formula, and succent expression of genaral purpose code.

With full integration into Dev Studio and its GUI/Web building tools, I think F# could be applied successfully to just about any problem, and do so with more succint and understandable code while at the same time taking advantge of more complex algorithms.

Here are some exerpts from various places describing F#:


APRESS Description of "Expert F#" (book)

While inspired by OCaml, F# isn't just another functional programming language. Drawing on many of the strengths of both OCaml and .NET, it's a general-purpose language ideal for real-world development. F# integrates functional, imperative, and object-oriented programming styles so you can flexibly and elegantly solve programming problems, and brings .NET development alive with interactive execution. Whatever your background, you'll find that F# is easy to learn, fun to use, and extraordinarily powerful. F# will help change the way you think about and go about programming.
The F# Home Page

F# is a programming language that provides the much sought-after combination of type safety, performance and scripting, with all the advantages of running on a high-quality, well-supported modern runtime system. F# gives you a combination of

The only language to provide a combination like this is F# (pronounced FSharp) - a scripted/functional/imperative/object-oriented programming language that is a fantastic basis for many practical scientific, engineering and web-based programming tasks. 

F# is a pragmatically-oriented variant of ML that shares a core language with OCaml. F# programs run on top of the .NET Framework. Unlike other scripting languages it executes at or near the speed of C# and C++, making use of the performance that comes through strong typing. Unlike many statically-typed languages it also supports many dynamic language techniques, such as property discovery and reflection where needed. F# includes extensions for working across languages and for object-oriented programming, and it works seamlessly with other .NET programming languages and tools.