I spent the last month on "vacation", working for a different company on a different product in a different programming language. It was actually quite a lot of fun; I'd like to take more such vacations (not least because, unlike the sort where one travels to a different country, I got paid to do it.)
I was working primarily in C#, a language I've not spent much time in till now. I was also working on Windows-specific user interface code, rather than the platform-independent systems-level code I normally write.
C# is a weird language. It feels to me like something of a kitchen-sink language: it's got a bit of practically every language idea I've ever heard of. Generics, function delegates, event handlers, closures, ... there are about five times as many keywords as Java has. Java is to C# as Spanish is to English.
There were a few things that I really liked: I did get pretty friendly with closures, for instance, and the language support for iterators is cool. Java still feels more elegant to me, though. There's just too many ways to skin the same cat in C#. And Java's collection and concurrency libraries are still way better.
The one thing I most disliked about C# isn't really a fault of the language as such: the naming conventions. In Java, by convention, we name types with capital letters; methods, variables, and packages with lower-case. This helps disambiguate some syntax that would otherwise be hard for humans to read (even though it doesn't bother the compiler at all). In C#, by convention, namespaces, types, and methods are all capitalized; fields and variables aren't. Properties, which are fields that have built-in getter and setter methods (so they can be accessed by assignment syntax), are capitalized. To my eye, it's hard to read and ugly.
To a compiler, none of these distinctions really make much difference; the differences between the .NET and Java virtual machines is pretty small. Programming languages, as I've said before, are a way for programmers to express ideas: they're for people, not computers. Esthetics matters.
If I were in St. Louis, I'd be attending this talk on the Fan programming language, which claims to be compilable to both virtual machines and to get rid of a lot of the uglifications of both Java and C#.