Here's an interesting interview with Simon Peyton-Jones (SPJ) on Haskell. SPJ wrote the defacto GHC compiler.
Clearly the isolation from side-effects that functions have - due to the immutablity of "variables" lends itself well to parallel programming. Interestingly, Haskell differs from other functional languages like Scheme and ML by virtue of it's lazy evaluation. An expression in Haskell is not evaluated until it is actually used by something.
The more I play with Haskell the more I like the programming paradigm it encompasses (each functional language has it's pros/cons). Functional programming certainly won't usurp imperative, O-O languages but IMHO it will play an increasingly large part in the coming years - especially with Microsoft helping it into the mainstream with the development of their "less-pure" functional language, F#. (SPJ works for Microsoft Research)