While I know that functional languages aren't the most commonly used for game writing, there are a lot of benefits associate with them that seem like they would be interesting in any programming context. Especially the ease of parallelization I would think could be very useful as focus is moving toward more and more processors.

Also, with F# as a new member of the .NET family, it can be used directly with XNA, for example, which lowers the threshold quite a bit, as opposed to going with LISP, Haskell, Erlang, etc.

If anyone has experience writing games with functional code, what has turned out to be the positives and negatives? What was it suited for, what not?

Edit: Finding it hard to decide that there's a single good answer for this, so it's probably better suited as a community wiki post.