I wrote a book a few years ago about Sun One Services (the name for their J2EE stack when it was an expensive product). Opening up Sun's stack for free use and making the source code available through the Glassfish project is a good thing, but there are already so many great free and open source J2EE stacks: Jonas, JBoss, Apache Geronimo, and Gluecode. Glassfish binaries are released weekly, but with limited testing. Who would have thought 4 years ago that J2EE stacks would be a free commodity item?