As I understand it, JDS is Gnome. And as I understand it, OpenSolaris will be using newer versions of Gnome whenever it will be available. Hence the beta status of Open Solaris.
The reason Solaris is not using KDE is because KDE is changing the API and stuff, making it hard to support KDE. Gnome is better in that aspect. This is what I heard. This message posted from opensolaris.org
