- Will this mean that Java Applets that hail from 1990's are dead and not worth going back to?
JavaFX and associated changes are an attempt to revitalize the applet space - applets were always dogged by poor plugin implementations and flakeu`y bridges into the browser. That's been improved - though still needs more work - but at last Sun has recognized it needed work and has done something about it. Applets are better positioned than they have ever been. Of the competition you mention - Flash, Air, and Silverlight - I think you missed out the key competitor - the browser/javascript - the browser makers are also addressing key platform weaknesses - javascript performance, ability to do arbitrary drawing ( ie canvas etc ). For low-end requirements I think a pure play browser approach is going to win out - for higher end graphics - JavaFX has a chance.
- Same with Java Desktop: What will be compelling for us Java Developers to use it rather than JavaFX?
As a big developer of Java Desktop apps, one of the things that's missing is a decent set of basic widgets and the time to play! It needs a killer table implementation - you can embedded swing but kinda what's the point. Now I could write my own by that's not really where I'm adding value in my kinda of job.