Except that I really don't like Windows XP... I could care less about it. I'm not going to go to all that trouble (including buying a copy of Windows XP; I'm not going to steal it) just to use a Java-based website. That's really the main crux of my initial point, that if you're using Java applets, you're probably turning away what could be some valuable users.
The problem is paravirtualization still isnt supported in the x64 kernel. So its still too slow to do heavy tasks in. And you still need lots of ram and cores if you want to do lots of simultaneous work.