I think that in the future the functional programming community will be at peak. currently I think that the functional communities are too small to beat the Java community.
the functional is easier to any person. any one can write a functional code. Erlang for example has a light VM that can make profit of multiprocessors availability. this doesn't depend on certain compiler that enables parallelism in Java or C.
if you don't care about performance, think about parallelism as simpler way to structure software in a domain where there is a lot of natural concurrency.
I read a paper "Structured Programming Using Processes" in which the author tried to prove that the Erlang was capable to support a personal accounting software application. Maybe you can take a look to it later.
also, I like to point to Yaws, Yaws is a HTTP high performance 1.1 webserver particularly well suited for dynamic-content webapplications. I ma really amazed by its performance.
well, but why Erlang is not widely used till now?
Well the world likes Java. the type safe language. Security in distributed Erlang is “all or nothing,” so when a node is authenticated to another, it can perform any operation.
process isolation is not complete, a process can flood another process with messages, or it can steal all the CPU cycles by entering into an infinite loop.