I had a great time writing a static site generator for my website. Initially I wrote it all in C# but I started writing specific components in F#. Currently the only F# portion is the sync-over-FTP feature but I do plan to convert a lot of the data processing portion to F# where if makes sense.

I do look forward to having opportunities to mix the two. C# + a gui framework and F# for the non-gui logic works really well in my experience.