IMO immutable has taken a step *backward* a few releases ago, and that's about all I've thought about it.
immutable string a = "lol"; auto b = replace(a, "lol", "rofl"); // used to work, now doesn't. The thing is the immutable works well with normal functions, but not with range templates. Ugh. Other than that, the system kinda works, but I find I don't use it very often, especially in classes. Perhaps that will change with inout being finished.
