>> * I actually don't think immutability is as key to concurrency as it gets hyped to be. Clojure which I've used and enjoyed does tend to get in your way with the immutability by default.*
I don't want to join into a language war, but I wanted to point out two things with this statement:
1- I can show you video lectures from 1985 that discuss mutability -vs- immutability in concurrent systems. Immutability won this war, at least in the research realm, 30 years ago.
2- Rich Hickey worked on massive telephone systems and created Clojure, at least in (large) part, out of frustration of dealing with mutation.
So there's a long line of research backed by "real world" experience showing mutation not holding up well for concurrency. Erlang is another example.
Regardless, I do agree that immutability may not be what it is hyped up to be, especially if you are looking for the mythical silver bullet, but it most certainly isn't over-hyped if you compare it to mutation, and the ideas are still quite young and being tested. Give it 20 years and I suspect there will be another paradigm shift at some point.