Don't get discouraged by the comments, your post is fair. I was a team lead at one of the companies mentioned by the OP, and using F# was a painful and ultimate

Don't get discouraged by the comments, your post is fair. I was a team lead at one of the companies mentioned by the OP, and using F# was a painful and ultimately a major failure, because of poor tooling and difficulties in hiring skilled developers in the language. It's not impossible to succeed, but there are a lot of ways to making it much harder -- one of this being choosing a niche language without a compelling reason to do so. There is nothing wrong with F#, the language (even though I don't particularly like its syntax), but clearly one has to account for the costs of reskilling the team on a new language, as well as a new paradigm, making a bet on a language with a still uncertain future (will it ever become a mainstream language?) and really non-existent tooling support. Given that both C# and F# are general purpose, hybrid languages, I don't see a compelling story -- in 2014 -- behind F# that makes it such as huge deal as its advocates make it. The onus is on them to bring convincing evidence to the table that, once factored in the risks and the costs that arise from the shortcomings, the benefits are still a good bargain in the real world, and with real people, outside of the easy fake example one finds on blogs etc.