>>Important to who? I use tools written in functional languages every single day.<< To the market. There are all kind of servers from web servers to database servers to other kinds of servers. Almost none are made using functional programming. Then, there is lot of software out there, which is made almost exclusively in C/C++, Java & .Net. Haskell & co. are only used in academia and by hobbyists (math people who can't learn proper programming)