C#/.Net seems like a solid language and framework but you are locked into Microsoft for just about everything. Java has so many frameworks and layers that it's hard to keep track of all of them. Then again, it has support from IBM, Oracle on the high-end and in the Open Source world and can be lightweight to almost overkill (EJB). Anybody have experiences to share in their job environments? I am curious myself.
I've been working with C# and the .Net Framework since it was in beta. We just delivered our first applicaion in a pretty complex SOA based around WCF (Windows Communication Framework) that will be our baseline for all of our future development efforts, at least for the forseeable future. I don't have any real experience with Java, so I can't really compare and contrast it with C#.
You might want to check out this: http://www.mono-project.com/Main_Page I've also been using .Net since the betas. I've only done a little Java, but I think the .Net libraries are far more consistent and easier to use. And the latest version of Visual Studio is just dreamy.
One of the things I really like about the .Net framework is its language independence. You can create applications and/or classes in C#, Managed C++, VB.Net, J#, Fortran, Cobol, Python, Delphi, etc, as long as the languages are CLR (Common Language Runtime) compliant. And the way the CLR is structured allows you to inherit a C# class from a VB.Net class, which could inherit from a Cobol.Net class, which could inherit from a C++ class. Very slick.
.NET here since "cool.exe", anybody remember that? IMO .NET vs Java is just another question of best tool for the job. Targeting only the Windows platforms? Go .NET, otherwise, go with Java.