Plus the hiring mentality is "oh no, we won't find an F# developer". The problem is that they're looking for "language" developers in the first place. Who the hell cares if a hire knows F#? If they don't but worth hiring, they'll easily learn it. This is true for most languages, but extra true for F# as you still have the CLR, the whole .NET Framework, Visual Studio, etc.
The biggest thing holding F# back apart from that, and apart from people that are well, scared of it, to put it kindly, has been .NET itself. Mono's been flaky for F# development I hear, and people have been suspicious of .NET overall, I feel. Though I do have long-running server apps at high volume working fine with F# on Mono on Linux, ASP.NET and other experiences are suboptimal.
With Microsoft's new stance on open source and shipping .NET everywhere, hopefully a lot more people will give it a spin. F#'s probably in the top spot for the combination of tooling, libraries, and language - so long as you don't mind GC.
As far as the language itself, it does a pretty good job at doing multi-paradigm. In fact, it does OO better than C# in some cases (object expressions).