Depends a lot on what type of software is b ing written. The people that keep beating the drums that Java = C# have not worked with the language extensively enough. So many things outside of basic languages constructs are different. Tooling is also a big hurdle to change too.
I've worked in both extensively, and there are certainly far more similarities than differences. I've put C# devs on to Java codebases and got them up to speed very quickly. But you still need to have Java pros that know all the gotchas etc. to do the code reviews.
