I\'ve been a web developer for some time now, and have recently started learning some functional programming. Like others, I\'ve had some significant trouble apply many of
Not at all. There are a genre of databases known as 'Functional Databases', of which Mnesia is perhaps the most accessible example. The basic principle is that functional programming is declarative, so it can be optimised. You can implement a join using List Comprehensions on persistent collections and the query optimiser can automagically work out how to implement the disk access.
Mnesia is written in Erlang and there is at least one web framework (Erlyweb) available for that platform. Erlang is inherently parallel with a shared-nothing threading model, so in certain ways it lends itself to scalable architectures.