So, here it is! Finally some details available to public and something real we (Open Solaris Pilot members) can talk about without NDA restrictions.
First as you can find on official Open Solaris site it's being released under OSI approved license: CDDL. So it's open, and yes you can fork (it looks like forking is important to some people). Let me repeat - it's under OSI approved license (means open) and you can fork.
Although only DTrace code is publicly available now, Pilot members have access to more code. We can actually build and boot system based on Open Solaris. Ben Rockwood has posted blog entry with a picture of running Open Solaris system which he compiled himself. Another Pilot member Jörg Schilling has posted similar blog entry - again booted system with compiled Open Solaris by him.
I wish I had a time... But I'll find some and definitely will compile my own Open Solaris, soon!
So, for all non-believers, etc. - Open Solaris is real! It's really happening!