According to this javac and hotspot will be open sourced at the end of this year. They also say they will open source the complete Java ME stack (this was the real surprise for me).
The complete stack of Java SE will be available at beginning of 2007, and as suspected some part will remain closed source due to licensing.
The actual license is unclear at this point, but seeing that Glassfish CDDL (Community Development and Distribution License) it would be a logical step.
For more information visit the official site over at java.net