Interpreted JavaFX Script, which the book is based upon, is quite stable (it hasn't changed since the book was written, and it also runs in a stable manner). For example, here's an example (Word Search Puzzle Builder) from the book, which includes a JNLP link so that you can run it: Spotting JavaFX Apps in the Wild - The Word Search Puzzle Builder
Compiled JavaFX Script is still in flux. I only use it for prototyping and creating utilities at this point. Based upon the progress that I've observed in the development of the JavaFX Script Compiler, I anticipate that a 1.0 release will happen in Q3 of 2008, at which point I'll begin writing production applications with compiled JavaFX Script.