I think the main answer to that question is 'exposure'.

Functional programming is nothing new, I was taught Haskell at university some 12 years ago and loved it. But rarely got to use the language in my professional work.

Recently there have been a number of languages gaining traction in the main stream that use a multi-paradigm approach; F#, JavaScript being prime examples.

JavaScript in particular, especially when used with a functional-style framework language like jQuery or Prototype, is becoming an everyday language for many people due to all the work on dynamic modern websites. This exposure to the functional style makes people realise the power it grants, especially when one is able to drop back to an imperative style at will.

One people are exposed, they try out more fully fledged variants of functional languages and start to use them for day-to-day tasks.

With F# becoming a first-class language in Visual Studio 2010 and jQuery (et al) becoming so important, it is becoming realistic to use these languages, rather than just something obscure to play with or make isolated programs.

Remember that code has to be maintainable - a critical mass of developers must use and support languages in order for companies to feel safe in using them.

I think the main answer to that question is 'exposure'.

Functional programming is nothing new, I was taught Haskell at university some 12 years ago and loved it. But rarely got to use the language in my professional work.

Recently there have been a number of languages gaining traction in the main stream that use a multi-paradigm approach; F#, JavaScript being prime examples.

JavaScript in particular, especially when used with a functional-style framework language like jQuery or Prototype, is becoming an everyday language for many people due to all the work on dynamic modern websites. This exposure to the functional style makes people realise the power it grants, especially when one is able to drop back to an imperative style at will.

Once people are exposed, they try out more fully fledged variants of functional languages and start to use them for day-to-day tasks.

With F# becoming a first-class language in Visual Studio 2010 and jQuery (et al) becoming so important, it is becoming realistic to use these languages, rather than just something obscure to play with or make isolated programs.

Remember that code has to be maintainable - a critical mass of developers must use and support languages in order for companies to feel safe in using them.