F# and MonoGame on the Mac. If you want to build games on the Mac, you have an interesting option with MonoGames. This is a reimplementation of the Microsoft XNA APIs. So basically, it's just the continuation of Mono into the gaming area. Pretty cool stuff - and because a cool thing alone isn't enough, the linked article provides the whole thing with integration in F#, the functional language for .NET from Microsoft. Unfortunately, for iOS, MonoTouch and for Android, MonoDroid are required, which means there is a slight hurdle to overcome in terms of acquisition (the licenses are not exactly cheap, so maybe not quite the knockout for hobbyists).
f#
Bistro. This is now a web framework for F#, inspired by Django (among others). Unfortunately not as lean as Scalatra or other micro-frameworks, but perhaps still worth a look.
Mixing it up: when F# meets C#. As you never program in a closed room, the connections between languages are quite important - and especially on platforms like .NET and JVM. The mappings of F# data types to C# data types and the use of these look quite interesting. Using C# data from F# is trivial, but the other way around there are some peculiarities. A similar situation exists with Scala and Java.
F Sharp Programming - Wikibooks, open books for an open world. Seems to be a quite nice basic overview of F# - so especially for those who don't already have prior experience (e.g. from OCAML).
Installing and using F# in MonoDevelop - a bit further down under "Installation Instructions" and look for the description for installing the F# MonoDevelop Plugin. Unfortunately, there are currently only templates for console projects with F# in the plugin.
F# cross-platform packages and samples - just look for the Mac Installer packages there (as of November 2010 Update) or above under "Download" (the link probably changes often when new releases come out). It's a simple Mac Installer, after which you have F# (OCaml for .Net) installed.