It's been no real secret that the .NET CLR (Common Language Runtime) has been Microsoft's answer to Java. Garbage collection, bytecode compilation, large set of core libraries, it's all there. But there is a problem that I've encountered recently: distribution size and install base.
A fairly clean Windows XP machine is fairly certain to not have anything higher than .NET 1.x installed. Anything really compelling in the .NET framework requires 3.5. This means somehow you need to get version 3.5 onto the machine somehow. This isn't a problem in Windows Vista and later, which include the framework. Microsoft's answer to simple deployment is it's "ClickOnce" system, where an application automatically installs .NET from the Internet (if necessary) before installing itself. Sure, it's a 60MB download, but it only needs to be done once.
The real issue is when you can't guarantee an Internet connection or a working .NET 3.5 installation. At this point you must resort to the offline installation, and this is where .NET and Java are very different. For Java 1.6 SE, the offline installer is 16MB for Windows 32-bit. For .NET 3.5, the offline installer is a 200MB universal package, with no way to cut out the parts you don't need. Java in fact is so small relatively speaking that many applications actually include the JRE in their package (for example OpenOffice - 148MB with JRE vs. 134MB without), whereas .NET can turn a 10MB application into a 210MB monstrosity.
Now in my particular situation, I'm embarassed to have chosen to use C#/.NET/WPF for a simple tool at work. For programming the tool itself, it was certainly the fastest option - other kinds of Windows programming, e.g. MFC or Forms, just look painful, and I thought the barrier to entry would be lower than Java. However this 1MB tool requires the 200MB .NET offline installer to be carted around with it because the network it's used on is completely separate from the Internet.
.NET will only be really appealing once it's ubiquitous, but then "critical mass" is one of the big problems for lots of software. For now, I think I'm going to try Java next time...