Last week I attended a Java User's group meeting where the topic of the discussion was "Java vs .NET". The speaker was Ted Neward, the author of Server-based Java programming. Interestingly enough, he was convinced that .Net is the way to go, and would pose a serious threat to Java in the future.
However I came back unimpressed. There is nothing in .NET and C# that Java can't do better. Sure there are a few interesting things in .NET, but it
does not have any new features which aren't already there in the computing world. Moreover most of the
good ideas have been stolen from Java.
M$ has this grand vision of doing everything and anything with .NET. But .NET is still a good one year from being released in it's final version (and another 4 yrs to sort out all the bugs that come along with it

). And unless you have something concrete which you can look at, it's anybody's guess what it might be. So for now I would simply dismiss it as pure marketing hype.
And the biggest disadvantage with .NET? Being tied to the Windows platform. I don't wanna be running .NET on Windows 2000 and see my server crash 10 times a day. I'd much rather use a good old Solaris box running a J2EE app server!