Even IF Java had a flash-level 98%+ adoption rate, the UI experience with Java applets in the real world has never been good in my experience. There is an annoying startup time before the apps load, Java sometimes crashes my browser, and the most ridiculous thing of all is that the last few 'advanced 3d' apps that I've tried running display a horrific security warning message saying that the app is untrusted. Apparently you can sign the apps to remove the warning, but why is it that people aren't always doing that? Is there some huge fee that Sun charges to sign your apps? I'm sorry but I'm not willing to give an untrusted browser app full access to my file system. Flash doesn't allow full access PERIOD (which definitely limits its usefulness in some applications) and I don't have to even worry before trying a new app.

Anyhow, I still haven't seen any compelling reasons to use Java that are so incredible that they outweigh these serious shortcomings. I think it's just a total non-starter. And with Flash starting to now support hardware 3D acceleration with Flash 10, there is one less reason to use Java.