The implementation is not complete, and I don’t know how true the 30x statement is, but the difference in the video is clear:
http://blog.joa-ebert.com/2010/08/19/introducing-jitb/
From the video, you may also notice that it’s based on LWJGL
impressive!
however I did notice a much worse startup time. Also, since its feature in-complete it may have an advantage speed wise.
With that said, I would expect a jvm based action script executor to be faster, simply because its much better than adobes VM
looks good.
Just noticed that its also just hit the slashdot front page http://developers.slashdot.org/story/10/08/20/1439207/Introducing-JITB-mdash-a-Flash-Player-Built-On-the-JVM
I dropped the chap a line, might be able to do some helping here.
Cas 
It may run on the JVM, but unfortunately it is written in Scala not Java.