Unfortunately, a lot of post-processors like PostSharp aren't smart enough to do that. Even though Visual Studio was only compiling once, PostSharp seemed to require a lot of time to do its thing.

I have seen environments for Java that could reload JAR-files. Perhaps DLLs are different, but that has little to do with a statically typed language.

I'd be interested if anyone knows of an environment for a statically typed language that could do this quickly and without losing run-time data.

In a dynamically typed language, altering the server environment at runtime incurs only the cost of evaluating the code. I can inject code at any point, redefine functions, query the state of the current data structures, and so forth. The entire environment is mutable; something that seems like it would be difficult to do with static types.